The Experts below are selected from a list of 22401 Experts worldwide ranked by ideXlab platform
Charles C Steidel - One of the best experts on this subject based on the ideXlab platform.
-
the rest frame ultraviolet spectra of uv selected active galactic nuclei at z 2 3
2011Co-Authors: Kevin N Hainline, Alice E Shapley, Jenny E Greene, Charles C SteidelAbstract:We present new results for a sample of 33 narrow-lined UV-selected active galactic nuclei (AGNs), identified in the course of a spectroscopic survey for star-forming galaxies at z ~ 2-3. The rest-frame UV composite spectrum for our AGN sample shows several emission lines characteristic of AGNs, as well as Interstellar Absorption features detected in star-forming Lyman break galaxies (LBGs). We report a detection of N iv] λ1486, which has been observed in high-redshift radio galaxies, as well as in rare optically selected quasars. The UV continuum slope of the composite spectrum is significantly redder than that of a sample of non-AGN UV-selected star-forming galaxies. Blueshifted Si iv Absorption provides evidence for outflowing highly ionized gas in these objects at speeds of ~10^3 km s^(–1), quantitatively different from what is seen in the outflows of non-AGN LBGs. Grouping the individual AGNs by parameters such as the Lyα equivalent width, redshift, and UV continuum magnitude allows for an analysis of the major spectroscopic trends within the sample. Stronger Lyα emission is coupled with weaker low-ionization Absorption, which is similar to what is seen in the non-AGN LBGs, and highlights the role that cool Interstellar gas plays in the escape of Lyα photons. However, the AGN composite does not show the same trends between Lyα strength and extinction seen in the non-AGN LBGs. These results represent the first such comparison at high redshift between star-forming galaxies and similar galaxies that host AGN activity.
-
the rest frame ultraviolet spectra of uv selected active galactic nuclei at z 2 3
2010Co-Authors: Kevin N Hainline, Alice E Shapley, Jenny E Greene, Charles C SteidelAbstract:We present new results for a sample of 33 narrow-lined UV-selected active galactic nuclei (AGNs), identified in the course of a spectroscopic survey for star-forming galaxies at z ~ 2-3. The rest-frame UV composite spectrum for our AGN sample shows several emission lines characteristic of AGNs, as well as Interstellar Absorption features seen in star-forming Lyman Break Galaxies (LBGs). We report a detection of NIV]1486, which has been observed in high-redshift radio galaxies, as well as in rare optically-selected quasars. The UV continuum slope of the composite spectrum is significantly redder than that of a sample of non-AGN UV-selected star forming galaxies. Blueshifted SiIV Absorption provides evidence for outflowing highly-ionized gas in these objects at speeds of ~ 10^(3) km/s, quantitatively different from what is seen in the outflows of non-AGN LBGs. Grouping the individual AGNs by parameters such as Ly-alpha equivalent width, redshift, and UV continuum magnitude allows for an analysis of the major spectroscopic trends within the sample. Stronger Ly-alpha emission is coupled with weaker low-ionization Absorption, which is similar to what is seen in the non-AGN LBGs, and highlights the role that cool Interstellar gas plays in the escape of Ly-alpha photons. However, the AGN composite does not show the same trends between Ly-alpha strength and extinction seen in the non-AGN LBGs. These results represent the first such comparison at high-redshift between star-forming galaxies and similar galaxies that host AGN activity.
-
a study of Interstellar gas and stars in the gravitationally lensed galaxy the cosmic eye from rest frame ultraviolet spectroscopy
2010Co-Authors: Anna M Quider, Max Pettini, Alice E Shapley, Charles C Steidel, Daniel P StarkAbstract:We report the results of a study of the rest-frame ultraviolet (UV) spectrum of the Cosmic Eye (J213512.73−010143) , a luminous (L∼ 2L*) Lyman break galaxy at z_(sys)= 3.07331 magnified by a factor of ~25 via gravitational lensing by foreground mass concentrations at z= 0.73 and 0.33. The spectrum, recorded at high resolution and signal-to-noise ratio with the Echellette Spectrograph and Imager (ESI) spectrograph on the Keck II telescope, is rich in Absorption features from the gas and massive stars in this galaxy. The Interstellar Absorption lines are resolved into two components of approximately equal strength and each spanning several hundred km s^(−1) in velocity. One component has a net blueshift of −70 km s^(−1) relative to the stars and H II regions and presumably arises in a galaxy-scale outflow similar to those seen in most star-forming galaxies at z= 2–3 . The other is more unusual in showing a mean redshift of +350 km s^(−1) relative to z_(sys); possible interpretations include a merging clump, or material ejected by a previous star formation episode and now falling back on to the galaxy, or more simply a chance alignment with a foreground galaxy. In the metal Absorption lines, both components only partially cover the OB stars against which they are being viewed. However, there must also be more pervasive diffuse gas to account for the near-total covering fraction of the strong damped Lyα line, indicative of a column density N(HI) = (3.0 ± 0.8) × 10^(21) cm^(−2) . We tentatively associate this neutral gas with the redshifted component, and propose that it provides the dust 'foreground screen' responsible for the low ratio of far-infrared to UV luminosities of the Cosmic Eye. The C IV P Cygni line in the stellar spectrum is consistent with continuous star formation with a Salpeter initial mass function, stellar masses from 5 to 100 M_⊙ , and a metallicity Z ~ 0.4 Z_⊙. Compared to other well-studied examples of strongly lensed galaxies, we find that the young stellar population of the Cosmic Eye is essentially indistinguishable from those of the Cosmic Horseshoe and MS 1512−cB58 . On the other hand, the Interstellar spectra of all three galaxies are markedly different, attesting to the real complexity of the interplay between starbursts and ambient Interstellar matter in young galaxies observed during the epoch when cosmic star formation was at its peak.
-
a study of Interstellar gas and stars in the gravitationally lensed galaxy the cosmic eye from rest frame ultraviolet spectroscopy
2009Co-Authors: Anna M Quider, Max Pettini, Alice E Shapley, Charles C Steidel, Daniel P StarkAbstract:We report the results of a study of the rest-frame UV spectrum of the Cosmic Eye, a luminous Lyman break galaxy at z=3.07331 gravitationally lensed by a factor of 25. The spectrum, recorded with the ESI spectrograph on the Keck II telescope, is rich in Absorption features from the gas and massive stars in this galaxy. The Interstellar Absorption lines are resolved into two components of approximately equal strength and each spanning several hundred km/s in velocity. One component has a net blueshift of -70 km/s relative to the stars and H II regions and presumably arises in a galaxy-scale outflow similar to those seen in most star-forming galaxies at z = 2-3. The other is more unusual in showing a mean redshift of +350 km/s relative to the systemic redshift; possible interpretations include a merging clump, or material ejected by a previous star formation episode and now falling back onto the galaxy, or more simply a chance alignment with a foreground galaxy. In the metal Absorption lines, both components only partially cover the OB stars against which they are being viewed. We tentatively associate the redshifted component with the strong damped Lyman alpha line, indicative of a column density N(H I) = (3.0 +/- 0.8) x 10(21) atoms/cm2, and propose that it provides the dust `foreground screen' responsible for the low ratio of far-infrared to UV luminosities of the Cosmic Eye. Compared to other well-studied examples of strongly lensed galaxies, we find that the young stellar population of the Cosmic Eye is essentially indistinguishable from those of the Cosmic Horseshoe and MS 1512-cB58, while the Interstellar spectra of all three galaxies are markedly different, attesting to the real complexity of the interplay between starbursts and ambient Interstellar matter in young galaxies (abridged).
-
the ultraviolet spectrum of the gravitationally lensed galaxy the cosmic horseshoe a close up of a star forming galaxy at z 2
2009Co-Authors: Anna Quider, Max Pettini, Alice E Shapley, Charles C SteidelAbstract:Taking advantage of strong gravitational lensing, we have recorded the rest-frame ultraviolet (UV) spectrum of the z= 2.38115 galaxy 'the Cosmic Horseshoe' (J1148+1930) at higher resolution and signal-to-noise ratio than is currently feasible for unlensed galaxies at z= 2–3 . With a star formation rate of ~100 M_⊙ yr^(−1) , dynamical mass M_vir≃ 1 × 10^(10) M_⊙ , half-solar metallicity and moderate reddening E(B−V) = 0.15 , the Cosmic Horseshoe is a good example of the population of galaxies responsible for most of the star formation activity at these redshifts. From the analysis of stellar spectral features we conclude that a continuous mode of star formation with a Salpeter slope for stars in the mass range 5–100 M_⊙ gives a good representation of the UV spectrum, ruling out significant departures from a 'standard' initial mass function. Generally, we find good agreement between the values of metallicity deduced from stellar and nebular tracers. Interstellar Absorption is present over a velocity range Δv≃ 1000 km s^(−1) , from −800 to +250 km s^(−1) relative to the stars and their H ii regions, but we still lack a model relating the kinematic structure of the gas to its location within the galaxy. There is evidence to suggest that the outflowing Interstellar gas is patchy, covering only ∼60 per cent of the UV stellar continuum. The Lyα line shares many of the characteristics of the so-called Lyα emitters; its double-peaked profile can be reproduced by models of Lyα photons resonantly scattered by an expanding shell of gas and dust, with ∼10–15 per cent of the photons escaping the galaxy. Many of the physical properties of the Cosmic Horseshoe are similar to those of the only other galaxy at z= 2–3 studied in comparable detail up to now: MS 1512−cB58. The fact that these two galaxies have drastically different Lyα lines may be due simply to orientation effects, or differences in the covering factor of outflowing gas, and cautions against classifying high-z galaxies only on the basis of spectral features, such as Lyα, whose appearance can be affected by a variety of different parameters.
Alice E Shapley - One of the best experts on this subject based on the ideXlab platform.
-
the rest frame ultraviolet spectra of uv selected active galactic nuclei at z 2 3
2011Co-Authors: Kevin N Hainline, Alice E Shapley, Jenny E Greene, Charles C SteidelAbstract:We present new results for a sample of 33 narrow-lined UV-selected active galactic nuclei (AGNs), identified in the course of a spectroscopic survey for star-forming galaxies at z ~ 2-3. The rest-frame UV composite spectrum for our AGN sample shows several emission lines characteristic of AGNs, as well as Interstellar Absorption features detected in star-forming Lyman break galaxies (LBGs). We report a detection of N iv] λ1486, which has been observed in high-redshift radio galaxies, as well as in rare optically selected quasars. The UV continuum slope of the composite spectrum is significantly redder than that of a sample of non-AGN UV-selected star-forming galaxies. Blueshifted Si iv Absorption provides evidence for outflowing highly ionized gas in these objects at speeds of ~10^3 km s^(–1), quantitatively different from what is seen in the outflows of non-AGN LBGs. Grouping the individual AGNs by parameters such as the Lyα equivalent width, redshift, and UV continuum magnitude allows for an analysis of the major spectroscopic trends within the sample. Stronger Lyα emission is coupled with weaker low-ionization Absorption, which is similar to what is seen in the non-AGN LBGs, and highlights the role that cool Interstellar gas plays in the escape of Lyα photons. However, the AGN composite does not show the same trends between Lyα strength and extinction seen in the non-AGN LBGs. These results represent the first such comparison at high redshift between star-forming galaxies and similar galaxies that host AGN activity.
-
the rest frame ultraviolet spectra of uv selected active galactic nuclei at z 2 3
2010Co-Authors: Kevin N Hainline, Alice E Shapley, Jenny E Greene, Charles C SteidelAbstract:We present new results for a sample of 33 narrow-lined UV-selected active galactic nuclei (AGNs), identified in the course of a spectroscopic survey for star-forming galaxies at z ~ 2-3. The rest-frame UV composite spectrum for our AGN sample shows several emission lines characteristic of AGNs, as well as Interstellar Absorption features seen in star-forming Lyman Break Galaxies (LBGs). We report a detection of NIV]1486, which has been observed in high-redshift radio galaxies, as well as in rare optically-selected quasars. The UV continuum slope of the composite spectrum is significantly redder than that of a sample of non-AGN UV-selected star forming galaxies. Blueshifted SiIV Absorption provides evidence for outflowing highly-ionized gas in these objects at speeds of ~ 10^(3) km/s, quantitatively different from what is seen in the outflows of non-AGN LBGs. Grouping the individual AGNs by parameters such as Ly-alpha equivalent width, redshift, and UV continuum magnitude allows for an analysis of the major spectroscopic trends within the sample. Stronger Ly-alpha emission is coupled with weaker low-ionization Absorption, which is similar to what is seen in the non-AGN LBGs, and highlights the role that cool Interstellar gas plays in the escape of Ly-alpha photons. However, the AGN composite does not show the same trends between Ly-alpha strength and extinction seen in the non-AGN LBGs. These results represent the first such comparison at high-redshift between star-forming galaxies and similar galaxies that host AGN activity.
-
a study of Interstellar gas and stars in the gravitationally lensed galaxy the cosmic eye from rest frame ultraviolet spectroscopy
2010Co-Authors: Anna M Quider, Max Pettini, Alice E Shapley, Charles C Steidel, Daniel P StarkAbstract:We report the results of a study of the rest-frame ultraviolet (UV) spectrum of the Cosmic Eye (J213512.73−010143) , a luminous (L∼ 2L*) Lyman break galaxy at z_(sys)= 3.07331 magnified by a factor of ~25 via gravitational lensing by foreground mass concentrations at z= 0.73 and 0.33. The spectrum, recorded at high resolution and signal-to-noise ratio with the Echellette Spectrograph and Imager (ESI) spectrograph on the Keck II telescope, is rich in Absorption features from the gas and massive stars in this galaxy. The Interstellar Absorption lines are resolved into two components of approximately equal strength and each spanning several hundred km s^(−1) in velocity. One component has a net blueshift of −70 km s^(−1) relative to the stars and H II regions and presumably arises in a galaxy-scale outflow similar to those seen in most star-forming galaxies at z= 2–3 . The other is more unusual in showing a mean redshift of +350 km s^(−1) relative to z_(sys); possible interpretations include a merging clump, or material ejected by a previous star formation episode and now falling back on to the galaxy, or more simply a chance alignment with a foreground galaxy. In the metal Absorption lines, both components only partially cover the OB stars against which they are being viewed. However, there must also be more pervasive diffuse gas to account for the near-total covering fraction of the strong damped Lyα line, indicative of a column density N(HI) = (3.0 ± 0.8) × 10^(21) cm^(−2) . We tentatively associate this neutral gas with the redshifted component, and propose that it provides the dust 'foreground screen' responsible for the low ratio of far-infrared to UV luminosities of the Cosmic Eye. The C IV P Cygni line in the stellar spectrum is consistent with continuous star formation with a Salpeter initial mass function, stellar masses from 5 to 100 M_⊙ , and a metallicity Z ~ 0.4 Z_⊙. Compared to other well-studied examples of strongly lensed galaxies, we find that the young stellar population of the Cosmic Eye is essentially indistinguishable from those of the Cosmic Horseshoe and MS 1512−cB58 . On the other hand, the Interstellar spectra of all three galaxies are markedly different, attesting to the real complexity of the interplay between starbursts and ambient Interstellar matter in young galaxies observed during the epoch when cosmic star formation was at its peak.
-
a study of Interstellar gas and stars in the gravitationally lensed galaxy the cosmic eye from rest frame ultraviolet spectroscopy
2009Co-Authors: Anna M Quider, Max Pettini, Alice E Shapley, Charles C Steidel, Daniel P StarkAbstract:We report the results of a study of the rest-frame UV spectrum of the Cosmic Eye, a luminous Lyman break galaxy at z=3.07331 gravitationally lensed by a factor of 25. The spectrum, recorded with the ESI spectrograph on the Keck II telescope, is rich in Absorption features from the gas and massive stars in this galaxy. The Interstellar Absorption lines are resolved into two components of approximately equal strength and each spanning several hundred km/s in velocity. One component has a net blueshift of -70 km/s relative to the stars and H II regions and presumably arises in a galaxy-scale outflow similar to those seen in most star-forming galaxies at z = 2-3. The other is more unusual in showing a mean redshift of +350 km/s relative to the systemic redshift; possible interpretations include a merging clump, or material ejected by a previous star formation episode and now falling back onto the galaxy, or more simply a chance alignment with a foreground galaxy. In the metal Absorption lines, both components only partially cover the OB stars against which they are being viewed. We tentatively associate the redshifted component with the strong damped Lyman alpha line, indicative of a column density N(H I) = (3.0 +/- 0.8) x 10(21) atoms/cm2, and propose that it provides the dust `foreground screen' responsible for the low ratio of far-infrared to UV luminosities of the Cosmic Eye. Compared to other well-studied examples of strongly lensed galaxies, we find that the young stellar population of the Cosmic Eye is essentially indistinguishable from those of the Cosmic Horseshoe and MS 1512-cB58, while the Interstellar spectra of all three galaxies are markedly different, attesting to the real complexity of the interplay between starbursts and ambient Interstellar matter in young galaxies (abridged).
-
the ultraviolet spectrum of the gravitationally lensed galaxy the cosmic horseshoe a close up of a star forming galaxy at z 2
2009Co-Authors: Anna Quider, Max Pettini, Alice E Shapley, Charles C SteidelAbstract:Taking advantage of strong gravitational lensing, we have recorded the rest-frame ultraviolet (UV) spectrum of the z= 2.38115 galaxy 'the Cosmic Horseshoe' (J1148+1930) at higher resolution and signal-to-noise ratio than is currently feasible for unlensed galaxies at z= 2–3 . With a star formation rate of ~100 M_⊙ yr^(−1) , dynamical mass M_vir≃ 1 × 10^(10) M_⊙ , half-solar metallicity and moderate reddening E(B−V) = 0.15 , the Cosmic Horseshoe is a good example of the population of galaxies responsible for most of the star formation activity at these redshifts. From the analysis of stellar spectral features we conclude that a continuous mode of star formation with a Salpeter slope for stars in the mass range 5–100 M_⊙ gives a good representation of the UV spectrum, ruling out significant departures from a 'standard' initial mass function. Generally, we find good agreement between the values of metallicity deduced from stellar and nebular tracers. Interstellar Absorption is present over a velocity range Δv≃ 1000 km s^(−1) , from −800 to +250 km s^(−1) relative to the stars and their H ii regions, but we still lack a model relating the kinematic structure of the gas to its location within the galaxy. There is evidence to suggest that the outflowing Interstellar gas is patchy, covering only ∼60 per cent of the UV stellar continuum. The Lyα line shares many of the characteristics of the so-called Lyα emitters; its double-peaked profile can be reproduced by models of Lyα photons resonantly scattered by an expanding shell of gas and dust, with ∼10–15 per cent of the photons escaping the galaxy. Many of the physical properties of the Cosmic Horseshoe are similar to those of the only other galaxy at z= 2–3 studied in comparable detail up to now: MS 1512−cB58. The fact that these two galaxies have drastically different Lyα lines may be due simply to orientation effects, or differences in the covering factor of outflowing gas, and cautions against classifying high-z galaxies only on the basis of spectral features, such as Lyα, whose appearance can be affected by a variety of different parameters.
Robert P Kirshner - One of the best experts on this subject based on the ideXlab platform.
-
variable sodium Absorption in a low extinction type ia supernova
2009Co-Authors: Joshua D Simon, A Galyam, Orly Gnat, Robert M Quimby, Mohan Ganeshalingam, Jeffrey M Silverman, Stephane Blondin, Alexei V Filippenko, Craig J Wheeler, Robert P KirshnerAbstract:Recent observations have revealed that some Type Ia supernovae exhibit narrow, time-variable Na I D Absorption features. The origin of the absorbing material is controversial, but it may suggest the presence of circumstellar gas in the progenitor system prior to the explosion, with significant implications for the nature of the supernova (SN) progenitors. We present the third detection of such variable Absorption, based on six epochs of high-resolution spectroscopy of the Type Ia supernova SN 2007le from the Keck I Telescope and the Hobby-Eberly Telescope. The data span a time frame of approximately three months, from 5 days before maximum light to 90 days after maximum. We find that one component of the NaID Absorption lines strengthened significantly with time, indicating a total column density increase of ~2.5 × 10^(12) cm^(–2). The data limit the typical timescale for the variability to be more than 2 days but less than 10 days. The changes appear to be most prominent after maximum light rather than at earlier times when the ultraviolet flux from the SN peaks. As with SN 2006X, we detect no change in the Ca II H and K Absorption lines over the same time period, rendering line-of-sight effects improbable and suggesting a circumstellar origin for the absorbing material. Unlike the previous two supernovae exhibiting variable Absorption, SN 2007le is not highly reddened (E_(B – V) = 0.27 mag), also pointing toward circumstellar rather than Interstellar Absorption. Photoionization calculations show that the data are consistent with a dense (10^7 cm^(–3)) cloud or clouds of gas located ~0.1 pc (3 × 10^(17) cm) from the explosion. These results broadly support the single-degenerate scenario previously proposed to explain the variable Absorption, with mass loss from a nondegenerate companion star responsible for providing the circumstellar gas. We also present possible evidence for narrow Hα emission associated with the SN, which will require deep imaging and spectroscopy at late times to confirm.
-
variable sodium Absorption in a low extinction type ia supernova
2009Co-Authors: Joshua D Simon, A Galyam, Orly Gnat, Robert M Quimby, Mohan Ganeshalingam, Jeffrey M Silverman, Stephane Blondin, Alexei V Filippenko, Craig J Wheeler, Robert P KirshnerAbstract:Recent observations have revealed that some Type Ia supernovae exhibit narrow, time-variable Na I D Absorption features. The origin of the absorbing material is controversial, but it may suggest the presence of circumstellar gas in the progenitor system prior to the explosion, with significant implications for the nature of the supernova progenitors. We present the third detection of such variable Absorption, based on six epochs of high-resolution spectroscopy of the Type Ia supernova SN 2007le from Keck and the HET. The data span ~3 months, from 5 days before maximum light to 90 days after maximum. We find that one component of the Na D Absorption lines strengthened significantly with time, indicating a total column density increase of ~2.5 x 10^12 cm^-2. The changes are most prominent after maximum light rather than at earlier times when the UV flux from the SN peaks. As with SN 2006X, we detect no change in the Ca II H&K lines over the same time period, rendering line-of-sight effects improbable and suggesting a circumstellar origin for the absorbing material. Unlike the previous two SNe exhibiting variable Absorption, SN 2007le is not highly reddened (E_B-V = 0.27 mag), also pointing toward circumstellar rather than Interstellar Absorption. Photoionization models show that the data are consistent with a dense (10^7 cm^-3) cloud or clouds of gas located ~0.1 pc from the explosion. These results broadly support the single-degenerate scenario previously proposed to explain the variable Absorption, with mass loss from a nondegenerate companion star responsible for providing the circumstellar gas. We also present tentative evidence for narrow Halpha emission associated with the SN, which will require followup observations at late times to confirm. [abridged]
Barry Y Welsh - One of the best experts on this subject based on the ideXlab platform.
-
new 3d gas density maps of nai and caii Interstellar Absorption within 300 pc
2010Co-Authors: Barry Y Welsh, R Lallement, J L Vergely, Severine RaimondAbstract:Aims. We present new high resolution (R > 50 000) Absorption measurements of the NaI doublet (5889-5895 A) along 482 nearby sight-lines, in addition to 807 new measurements of the CaII K (3933 A) Absorption line. We have combined these new data with previously reported measurements to produce a catalog of Absorptions towards a total of 1857 early-type stars located within 800 pc of the Sun. Using these data we have determined the approximate 3-dimensional spatial distribution of neutral and partly ionized Interstellar gas density within a distance-cube of 300 pc from the Sun. Methods. All newly recorded spectra were analyzed by means of a multi-component line profile-fitting program, in most cases using simultaneous fits to the line doublets. Normalized Absorption profiles were fitted by varying the velocity, doppler width and column density for all intervening Interstellar clouds. The resulting total column densities were then used in conjunction with the Hipparcos distances of the target stars to construct inversion maps of the 3D spatial density distribution of the NaI and CaII bearing gas. Results. A plot of the equivalent width of NaI versus distance reveals a wall of neutral gas at ~80 pc that can be associated with the boundary wall to the central rarefied Local Cavity region. In contrast, a similar plot for the equivalent width of CaII shows no sharply increasing Absorption at 80 pc, but instead we observe a slowly increasing value of CaII equivalent width with increasing sight-line distance sampled. Low values for the volume density of NaI ( > 10-10 cm-3 are found for sight-lines with distance >300 pc. Both high and low values of the volume density of CaII () are found for sight-lines 100 pc a value of ~ 10-9 cm-3 is typical for most sight-lines, indicating that the distribution of CaII bearing gas is fairly uniform throughout the general ISM. Our three maps of the 3D spatial distribution of local neutral NaI Absorption extend and improve upon the accuracy of similar maps initially presented by Lallement et al. (2003, A&A, 411, 447), with many new neutral Interstellar gas features (such as low neutral density gas tunnels) in the local Interstellar medium now being revealed for the first time. The maps of the 3D distribution of partially ionized CaII gas are the first of their kind to be presented and exhibit many spatial similarities to those of their equivalent NaI Absorption maps. A major finding from both sets of maps is that the low density Local Cavity region is surrounded by a highly fragmented wall of higher density NaI and CaII gas clouds. The appearance of this broken boundary may be linked to the purported explosive origin of the Local Cavity. Maps of the distribution of CaII gas density reveal the presence of many partially ionized low density cloudlets that reside within the Local Cavity, and their newly derived 3D spatial contours confirm previous observations of the local gas by Redfield & Linsky (2008, ApJ, 673, 283). Both the NaI and CaII maps suggest that the Local Cavity may contain several low density sub-cavities that are surrounded by thin filaments of neutral and/or partially ionized gas. However, further observations will be required to confirm the existence of a collection of cell-like Interstellar cavities. The new maps also reveal several sight-lines where CaII Absorption is high and the corresponding NaI Absorption is low, and vice-versa. Such regions are probably influenced by the effects of the local stellar ionization field which can significantly affect the observed NaI/CaII column density ratio. Plots of this ratio as a function of distance for stars located near to the galactic plane show values in the range 0.1 to 1.0 for sight-lines with distances <80 pc. However, ratio values of between 0.5 and 20 are typical for more distant sight-lines. The highest values of the NaI/CaII ratio are found towards ~ 150 in the direction of the Taurus dark clouds, with ratio values in the narrower range of 0.1 to 5 being found in galactic quadrant 3
-
new 3 d gas density maps of nai and caii Interstellar Absorption within 300pc
2009Co-Authors: Barry Y Welsh, R Lallement, J L Vergely, Severine RaimondAbstract:We present new high resolution (R>50,000) Absorption measurements of the NaI doublet (5889 - 5895A) along 482 nearby sight-lines, in addition to 807 new measurements of the CaII K (3933A) Absorption line. We have combined these new data with previously reported measurements to produce a catalog of Absorptions towards a total of 1857 early-type stars located within 800pc of the Sun. Using these data we have determined the approximate 3-dimensional spatial distribution of neutral and partly ionized Interstellar gasdensity within a distance-cube of 300pc from the Sun. All newly recorded spectra were analyzed by means of a multi-component line profile-fitting program, in most cases using simultaneous fits to the line doublets. Normalized Absorption profiles were fitted by varying the velocity, doppler width and column density for all intervening Interstellar clouds. The resulting total column densities were then used in conjunction with the Hipparcos distances of the target stars to construct inversion maps of the 3-D spatial density distribution of the NaI and CaII bearing gas. A plot of the equivalent width of NaI versus distance reveals a wall of neutral gas at ~80pc that can be associated with the boundary wall to the central rarefied Local Cavity region. In contrast, a similar plot for the equivalent width of CaII shows no sharply increasing Absorption at 80pc, but instead we observe a slowly increasing value of CaII equivalent width with increasing sight-line distance sampled.
-
intermediate velocity gas observed towards the shajn 147 snr
2004Co-Authors: S Sallmen, Barry Y WelshAbstract:We present high-resolution spectra (R ∼ 3k m s −1 ) of the Interstellar Na and Ca Interstellar Absorption lines observed towards 3 early-type stars with distances of 360 to 1380 pc along the line-of-sight towards the 800 pc distant Shajn 147 (S147) Supernova Remnant (SNR). These data are supplemented with far-UV (912-1180 A) aborption spectra of HD 36665 and HD 37318 recorded with the NASA Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. The observations reveal intermediate-velocity (IV) Absorption features at Vhelio =+ 92 km s −1 towards HD 37318 and at Vhelio = −65 and −52 km s −1 towards HD 36665, in addition to several other gas cloud components with lower velocity. These IV components can be associated with the expansion of the SNR that has disrupted the surrounding Interstellar gas. The IV component at V =+ 92 km s −1 seen towards HD 37318 was detected only in the far-UV lines of Fe and N , suggesting that it is composed mainly of warm and ionized gas. The two IV components observed towards HD 36665 were detected in Na ,C a ,N ,N ,O and Fe , indicating that it is composed of both neutral and ionized gas shells. Highly ionized gas was detected in the O λ 1032 A Absorption line at V ∼ +40 km s −1 towards both stars. This hot and highly ionized gas component is characterized by a columnn density ratio of N(C )/N(O ) < 0.27, which is consistent with that predicted by current models of evolved SNRs. However, we cannot preclude its origin in the Interstellar medium in line-of-sight to S147. Column-density ratios of (Mg/Fe), (Al/Si),(Si/Fe), (N/Fe), (O/Fe) and (Na/Ca) have been derived for the IV gas components detected towards S147. Similar ratios have also been derived for fast-moving gas observed towards two other SNRs in order to gain some insight into the behavior of element abundances in the disturbed Interstellar gas associated with these regions. In all cases except for Na and Ca, these elements appear to be present with near-solar abundance ratios.
-
high velocity nai and caii Absorption components observed towards the ic 443 snr
2003Co-Authors: Barry Y Welsh, S SallmenAbstract:We present high-resolution spectra (R 1: 8k m s 1 ) of the Interstellar NaI and CaII Interstellar Absorption lines observed towards 4 early-type stars with distances of 900-1500 pc in the line-of-sight towards the IC 443 Supernova Remant (SNR). The spectra of two of these stars (HD 43582 and HD 254577) exhibit a very complex pattern of Absorption with cloud components covering a total velocity range of 100 km s 1 to+50 km s 1 . The relative Absorption strength of many of the higher velocity components is highly variable between these two stars, suggesting that the disturbed Interstellar gas in this region possesses significant density gradients and/or large dierences in ionization and element depletion. In addition, we have detected three additional high-velocity components at Vhelio = 97:5, 84.0 and 67.6 km s 1 solely in their CaII lines, suggesting that the very highest velocity gas is more ionized and/or warmer than the lower velocity components or it has a highly variable level of gas phase element abundances. The column density ratios of NaI/CaII for the higher velocity cloud components are all<0.2, which is consistent with apprecia- ble levels of dust grain destruction due to Interstellar shocks caused by interaction of the expanding SNR blast-wave with the ambient Interstellar medium. The distance to IC 443 is confirmed at 1500 pc, which places the remnant at a similar distance to the Gem OB1 stellar association. Finally we note that the model of Chevalier (1999), in which the SNR is expanding into a clumpy Interstellar medium, can best reproduce the observed patterns of both emission and Absorption.
M Hlond - One of the best experts on this subject based on the ideXlab platform.
-
neutral Interstellar helium parameters based on ibex lo observations and test particle calculations
2012Co-Authors: M Bzowski, Marzena A Kubiak, P Bochsler, T Leonard, D Heirtzler, H Kucharek, J M Sokol, E Moebius, M HlondAbstract:Neutral Interstellar Helium (NISHe) is almost unaffected at the heliospheric interface with the Interstellar medium and freely enters the solar system. It provides some of the best information on the characteristics of the Interstellar gas in the Local Interstellar Cloud. The Interstellar Boundary Explorer (IBEX) is the second mission to directly detect NISHe. We present a comparison between recent IBEX NISHe observations and simulations carried out using a well-tested quantitative simulation code. Simulation and observation results compare well for times when measured fluxes are dominated by NISHe (and contributions from other species are small). Differences between simulations and observations indicate a previously undetected secondary population of neutral helium, likely produced by interaction of Interstellar helium with plasma in the outer heliosheath. Interstellar neutral parameters are statistically different from previous in situ results obtained mostly from the GAS/Ulysses experiment, but they do agree with the local Interstellar flow vector obtained from studies of Interstellar Absorption: the newly-established flow direction is ecliptic longitude 79.2 deg, latitude -5.1 deg, the velocity is \sim 22.8 km/s, and the temperature is 6200 K. These new results imply a markedly lower absolute velocity of the gas and thus significantly lower dynamic pressure on the boundaries of the heliosphere and different orientation of the Hydrogen Deflection Plane compared to prior results from Ulysses. A different orientation of this plane also suggests a new geometry of the Interstellar magnetic field and the lower dynamic pressure calls for a compensation by other components of the pressure balance, most likely a higher density of Interstellar plasma and strength of Interstellar magnetic field.
-
neutral Interstellar helium parameters based on ibex lo observations and test particle calculations
2012Co-Authors: M Bzowski, Marzena A Kubiak, E Mobius, P Bochsler, T Leonard, D Heirtzler, H Kucharek, J M Sokol, M HlondAbstract:Because of its high ionization potential and weak interaction with hydrogen, neutral Interstellar helium (NISHe) is almost unaffected at the heliospheric interface with the Interstellar medium and freely enters the solar system. This second most abundant species provides some of the best information on the characteristics of the Interstellar gas in the local Interstellar cloud. The Interstellar Boundary Explorer (IBEX) is the second mission to directly detect NISHe. We present a comparison between recent IBEX NISHe observations and simulations carried out using a well-tested quantitative simulation code. Simulation and observation results compare well for times when measured fluxes are dominated by NISHe (and contributions from other species are small). Differences between simulations and observations indicate a previously undetected secondary population of neutral helium, likely produced by interaction of Interstellar helium with plasma in the outer heliosheath. Interstellar neutral parameters are statistically different from previous in situ results obtained mostly from the GAS/Ulysses experiment, but they do agree with the local Interstellar flow vector obtained from studies of Interstellar Absorption: the newly established flow direction is ecliptic longitude 792, latitude –51, the velocity is ~22.8 km s–1, and the temperature is 6200 K. These new results imply a markedly lower absolute velocity of the gas and thus significantly lower dynamic pressure on the boundaries of the heliosphere and different orientation of the Hydrogen Deflection Plane compared to prior results from Ulysses. A different orientation of this plane also suggests a new geometry of the Interstellar magnetic field, and the lower dynamic pressure calls for a compensation by other components of the pressure balance, most likely a higher density of Interstellar plasma and strength of Interstellar magnetic field.
