- ID:
- ivo://CDS.VizieR/J/MNRAS/428/3355
- Title:
- Hydrogen volume densities in nearby galaxies
- Short Name:
- J/MNRAS/428/3355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a simple model of photodissociated atomic hydrogen on a galactic scale, it is possible to derive total hydrogen volume densities. These densities, obtained through a combination of atomic hydrogen, far-ultraviolet and metallicity data, provide an independent probe of the combined atomic and molecular hydrogen gas in galactic discs. We present a new, flexible and fully automated procedure using this simple model. This automated method will allow us to take full advantage of a host of available data on galaxies in order to calculate the total hydrogen volume densities of the giant molecular clouds surrounding sites of recent star formation. Until now this was only possible on a galaxy-by-galaxy basis using by-eye analysis of candidate photodissociation regions. We test the automated method by adopting various models for the dust-to-gas ratio and comparing the resulting densities for M74, including a new metallicity map of M74 produced by integral field spectroscopy. We test the procedure against previously published M83 volume densities based on the same method and find no significant differences. The range of total hydrogen volume densities obtained for M74 is approximately 5-700cm^-3^. Different dust-to-gas ratio models do not result in measurably different densities. The cloud densities presented here mean that M74 is added to the list of galaxies analysed using the assumption of photodissociated atomic hydrogen occurring near sites of recent star formation, and consolidate the method. For the first time, full metallicity maps are included in the analysis as opposed to metallicity gradients. The results will need to be compared with other tracers of the interstellar medium and photodissociation regions, such as CO and CII, in order to test our basic assumptions, specifically our assumption that the HI we detect originates in photodissociation regions.
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- ID:
- ivo://CDS.VizieR/J/A+A/562/A70
- Title:
- Imaging GRB 980425 in millimetic and submm
- Short Name:
- J/A+A/562/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gamma-ray bursts (GRBs) have been proposed as a tool to study star formation in the Universe, so it is crucial to investigate whether their host galaxies and immediate environments are in any way special compared with other star-forming galaxies. Here we present spatially resolved maps of dust emission of the host galaxy of the closest known GRB 980425 at z=0.0085 using our new high-resolution observations from Herschel, APEX, ALMA and ATCA. We modeled the spectral energy distributions of the host and of the star-forming region displaying the Wolf-Rayet signatures in the spectrum (WR region), located 800pc away from the GRB position. The host is characterised by low dust content and high fraction of UV-visible star-formation, similar to other dwarf galaxies. Such galaxies are abundant in the local universe, so it is not surprising to find a GRB in one of them, assuming the correspondence between the GRB rate and star-formation. The WR region contributes substantially to the host emission at the far-infrared, millimeter and radio wavelengths and we propose this to be a consequence of its high gas density. If dense environments are also found close to the positions of other GRBs, then the ISM density should also be considered as an important factor influencing whether a given stellar population can produce a GRB, in a similar way as metallicity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/367/1478
- Title:
- Interstellar NaI, TiII & CaIIK obs.
- Short Name:
- J/MNRAS/367/1478
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of interstellar NaI ({lambda}_air_=3302.37 and 3302.98{AA}), TiII ({lambda}_air_=3383.76{AA}) and CaIIK ({lambda}_air_=3933.66{AA}) absorption features for 74 sightlines towards O- and B-type stars in the Galactic disc. The data were obtained from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project (UVES POP), at a spectral resolution of 3.75km/s and with mean signal-to-noise ratios per pixel of 260, 300 and 430 for the NaI, TiII and CaII observations, respectively. Interstellar features were detected in all but one of the TiII sightlines and all of the CaII sightlines. The dependence of the column density of these three species with distance, height relative to the Galactic plane, HI column density, reddening and depletion relative to the solar abundance has been investigated. We also examine the accuracy of using the NaI column density as an indicator of that for HI. In general, we find similar strong correlations for both Ti and Ca, and weaker correlations for Na. Our results confirm the general belief that Ti and Ca occur in the same regions of the interstellar medium (ISM) and also that the TiII/CaII ratio is constant over all parameters. We hence conclude that the absorption properties of Ti and Ca are essentially constant under the general ISM conditions of the Galactic disc.
- ID:
- ivo://CDS.VizieR/J/AJ/159/216
- Title:
- Ions density in the CGM of low mass galaxy groups
- Short Name:
- J/AJ/159/216
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore how environment affects the metallicity of the circumgalactic medium (CGM) using 13 low-mass galaxy groups (two to five galaxies) at <z_abs_>=0.25 identified near background quasars. Using quasar spectra from the Hubble Space Telescope/Cosmic Origins Spectrograph (HST/COS) and from Keck/High Resolution Echelle Spectrometer (Keck/HIRES) or the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph (VLT/UVES), we measure column densities of or determine limits on CGM absorption lines. We use a Markov Chain Monte Carlo approach with Cloudy to estimate metallicities of cool (T~104K) CGM gas within groups and compare them to CGM metallicities of 47 isolated galaxies. Both group and isolated CGM metallicities span a wide range (-2<[Si/H]<0), where the mean group (-0.54{pm}0.22) and isolated (-0.77{pm}0.14) CGM metallicities are similar. Group and isolated environments have similar distributions of HI column densities as a function of impact parameter. However, contrary to isolated galaxies, we do not find an anticorrelation between HI column density and the nearest group galaxy impact parameter. We additionally divided the groups by member luminosity ratios (i.e., galaxy-galaxy and galaxy-dwarf groups). While there was no significant difference in their mean metallicities, a modest increase in sample size should allow one to statistically identify a higher CGM metallicity in galaxy-dwarf groups compared to galaxy-galaxy groups. We conclude that either environmental effects have not played an important role in the metallicity of the CGM at this stage and expect that this may only occur when galaxies are strongly interacting or merging or that some isolated galaxies have higher CGM metallicities due to past interactions. Thus, environment does not seem to be the cause of the CGM metallicity bimodality.
- ID:
- ivo://CDS.VizieR/J/AJ/136/479
- Title:
- IRAC observations of M83 extended UV disk
- Short Name:
- J/AJ/136/479
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spitzer Infrared Array Camera (IRAC) observations of two fields in the extended UV disk (XUV-disk) of M83 have been recently obtained, ~3R_HII_ away from the center of the galaxy (R_HII_=6.6kpc). Galaxy Evolution Explorer (GALEX) UV images have shown the two fields to host in situ recent star formation. The IRAC images are used in conjunction with GALEX data and new HI imaging from The HI Nearby Galaxy Survey (THINGS) to constrain stellar masses and ages of the UV clumps in the fields, and to relate the local recent star formation to the reservoir of available gas. Multi-wavelength photometry in the UV and mid-IR (MIR) bands of 136 UV clumps (spatial resolution >220pc) identified in the two target fields, together with model fitting of the stellar UV-MIR spectral energy distributions (SEDs), suggests that the clumps cover a range of ages between a few Myr and >1Gyr with a median value around <=100Myr, and have masses in the range 10^3^-3x10^6^M_{sun}_, with a peak ~10^4.7^M_{sun}.
- ID:
- ivo://CDS.VizieR/J/ApJ/679/140
- Title:
- IR measurement of quasar obscuration
- Short Name:
- J/ApJ/679/140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent work has suggested that the fraction of obscured AGNs declines with increasing luminosity, but it has been difficult to quantify this trend. Here we attempt to measure this fraction as a function of luminosity by studying the ratio of mid-infrared to intrinsic nuclear bolometric luminosity in unobscured AGNs. Because the mid-infrared is created by dust reprocessing of shorter wavelength nuclear light, this ratio is a diagnostic of f_obsc_, the fraction of solid angle around the nucleus covered by obscuring matter. In order to eliminate possible redshift dependences while also achieving a large dynamic range in luminosity, we have collected archival 24um MIPS photometry from objects with z~1 in the Sloan Digital Sky Survey DR5, the Great Observatories Origins Deep Survey, and the Cosmic Evolution Survey. To measure the bolometric luminosity for each object, we used archival optical data supplemented by GALEX data.
- ID:
- ivo://CDS.VizieR/J/ApJ/890/119
- Title:
- Iron element abundances in 3 very metal-poor stars
- Short Name:
- J/ApJ/890/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained new detailed abundances of the Fe-group elements Sc through Zn (Z=21-30) in three very metal-poor ([Fe/H]~-3) stars: BD+03 740, BD-13 3442, and CD-33 1173. High-resolution ultraviolet Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra in the wavelength range 2300-3050{AA} were gathered, and complemented by an assortment of optical echelle spectra. The analysis featured recent laboratory atomic data for a number of neutral and ionized species for all Fe-group elements except Cu and Zn. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys indicates that they are positively correlated in stars with [Fe/H]<=-2. The abundances of these elements in BD+03 740, BD-13 3442, CD-33 1173, and HD 84937 (studied in a previous paper of this series) are in accord with these trends and lie at the high end of the correlations. Six elements have detectable neutral and ionized features, and generally their abundances are in reasonable agreement. For Cr we find only minimal abundance disagreement between the neutral (mean of [CrI/Fe]=+0.01) and ionized species (mean of [CrII/Fe]=+0.08), unlike most studies in the past. The prominent exception is Co, for which the neutral species indicates a significant overabundance (mean of [CoI/H]=-2.53), while no such enhancement is seen for the ionized species (mean of [CoII/H]=-2.93). These new stellar abundances, especially the correlations among Sc, Ti, and V, suggest that models of element production in early high-mass metal-poor stars should be revisited.
- ID:
- ivo://CDS.VizieR/J/ApJ/652/1554
- Title:
- Iron in hot DA white dwarfs
- Short Name:
- J/ApJ/652/1554
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the iron abundance pattern in hot, hydrogen-rich (DA) white dwarfs. The study is based on new and archival far-ultraviolet spectroscopy of a sample of white dwarfs in the temperature range 30000K<=Teff<=64000K. The spectra obtained with the Far Ultraviolet Spectroscopic Explorer, along with spectra obtained with the Hubble Space Telescope Imaging Spectrograph and the International Ultraviolet Explorer, sample FeIII-FeVI absorption lines, enabling a detailed iron abundance analysis over a wider range of effective temperatures than previously afforded.
- ID:
- ivo://CDS.VizieR/J/ApJ/826/209
- Title:
- IRX-{beta} relation of HII regions in NGC628
- Short Name:
- J/ApJ/826/209
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been found that the infrared-to-ultraviolet luminosity ratio (IRX) and ultraviolet spectral slope ({beta}) have a tight correlation in starburst galaxies, while in normal galaxies the relation is deviated and has a much larger scatter. Star formation regions are much simpler in both morphology and physical properties than galaxies, so their photometric and spectroscopic properties are more easily and accurately determined. We have used the integral field spectroscopy and multiband photometric images to study the IRX-{beta} relation of HII regions in a nearby galaxy, NGC 628. There are obvious correlations between the D_n_ (4000), stellar population age, star formation rate, especially H{alpha} equivalent width EW(H{alpha}), and deviation distance d_p_ from the starburst IRX-{beta} relation. However, there is little correlation between the Balmer decrement, metallicity, and d_p_. It is much more complicated than expected, so that we cannot introduce a single second parameter to describe the scatter and deviation of the HII region IRX-{beta} relation.
- ID:
- ivo://CDS.VizieR/J/ApJS/136/631
- Title:
- IUE absorption toward 164 early-type stars
- Short Name:
- J/ApJS/136/631
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present measurements of Galactic interstellar AlIII, SiIV, and CIV absorption recorded in high-resolution archival ultraviolet spectra of 164 hot early-type stars observed by the International Ultraviolet Explorer (IUE) satellite. The objects studied were drawn from the list of hot stars scheduled to be observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite as part of observing programs designed to investigate absorption by OVI in the Galactic disk and halo. Multiple IUE echelle-mode integrations have been combined to produce a single ultraviolet (1150-1900{AA}) spectrum of each star with a spectral resolution of ~25km/s (FWHM). Selected absorption-line profiles are presented for each star along with plots of the apparent column density per unit velocity for each line of the AlIII, SiIV, and CIV doublets. We report absorption-line equivalent widths, absorption velocities, and integrated column densities based on the apparent optical depth method of examining interstellar absorption lines. We also determine column densities and Doppler parameters from single-component curve-of-growth analyses. The scientific analysis of these observations will be undertaken after the FUSE satellite produces similar measurements for absorption by interstellar OIV, FeIII, SIII, and other ions.
