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Start Over Subject ultraviolet astronomy
181. HST and UV photometry of NGC 6822
ID:
ivo://CDS.VizieR/J/AJ/132/378
Title:
HST and UV photometry of NGC 6822
Short Name:
J/AJ/132/378
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Hubble Space Telescope WFPC2 and STIS imaging of the low-metallicity galaxy NGC 6822, performed as part of a study of the young stellar populations in the galaxies of the Local Group. Eleven WFPC2 pointings, with some overlap, cover two regions extending over 19 and 13arcmin^2^, respectively, off the galaxy center. The filters used are F170W, F255W, F336W, F439W, and F555W. One 25x25 field observed with the STIS FUV- and NUV-MAMA includes Hodge's OB 8 association and the HII region Hubble V, contained in field 1 of Bianchi et al. (2001, Cat. <J/AJ/121/2020>); this previous study provides additional WFPC2 four-band photometry. We derive the physical parameters of the stars in the fields and the extinction by comparing the photometry to grids of model magnitudes.
182. HST & Chandra obs. of elliptical galaxies
ID:
ivo://CDS.VizieR/J/ApJS/248/31
Title:
HST & Chandra obs. of elliptical galaxies
Short Name:
J/ApJS/248/31
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate X-ray binary (XRB) luminosity function (XLF) scaling relations for Chandra-detected populations of low-mass XRBs (LMXBs) within the footprints of 24 early-type galaxies. Our sample includes Chandra and Hubble Space Telescope observed galaxies at D<~25Mpc that have estimates of the globular cluster (GC) specific frequency (S_N_) reported in the literature. As such, we are able to directly classify X-ray-detected sources as being coincident with unrelated background/foreground objects, GCs, or sources that are within the fields of the galaxy targets. We model the GC and field LMXB population XLFs for all galaxies separately and then construct global models characterizing how the LMXB XLFs vary with galaxy stellar mass and S_N_. We find that our field LMXB XLF models require a component that scales with S_N_ and has a shape consistent with that found for the GC LMXB XLF. We take this to indicate that GCs are "seeding" the galactic field LMXB population, through the ejection of GC LMXBs and/or the diffusion of the GCs in the galactic fields themselves. However, we also find that an important LMXB XLF component is required for all galaxies that scales with stellar mass, implying that a substantial population of LMXBs are formed "in situ," which dominates the LMXB population emission for galaxies with S_N_<~2. For the first time, we provide a framework quantifying how directly associated GC LMXBs, GC-seeded LMXBs, and in situ LMXBs contribute to LMXB XLFs in the broader early-type galaxy population.
183. HST/COS and FUSE UV spectra of Mrk 509
ID:
ivo://CDS.VizieR/J/A+A/623/A82
Title:
HST/COS and FUSE UV spectra of Mrk 509
Short Name:
J/A+A/623/A82
Date:
21 Oct 2021
Publisher:
CDS
Description:
To elucidate the location, physical conditions, mass outflow rate, and kinetic luminosity of the outflow from the active nucleus of the Seyfert 1 galaxy Mrk 509 we used coordinated ultraviolet and X-ray spectral observations in 2012 to followup our lengthier campaign conducted in 2009. We observed Mrk 509 with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) on 2012-09-03 and 2012-10-11 coordinated with X-ray observations using the High Energy Transmission Grating on the Chandra X-ray Observatory. Our far-ultraviolet spectra used grating G140L on COS to cover wavelengths from 920-2000{AA} at a resolving power of 2000, and gratings G130M and G160M to cover 1160-1750{AA} at a resolving power of 15000. We detect variability in the blue-shifted UV absorption lines on timescales spanning 3-12 years. The inferred densities in the absorbing gas are greater than logn[cm^-3^]~3. For ionization parameters ranging over logU=-1.5 to -0.2, we constrain the distances of the absorbers to be closer than 220pc to the active nucleus. The impact on the host galaxy appears to be confined to the nuclear region.
184. HST/COS observations of QSOs within 600kpc of M31
ID:
ivo://CDS.VizieR/J/ApJ/804/79
Title:
HST/COS observations of QSOs within 600kpc of M31
Short Name:
J/ApJ/804/79
Date:
21 Oct 2021
Publisher:
CDS
Description:
We demonstrate the presence of an extended and massive circumgalactic medium (CGM) around Messier 31 using archival HST Cosmic Origins Spectrograph ultraviolet spectroscopy of 18 QSOs projected within two virial radii of M31 (R_vir_=300kpc). We detect absorption from SiIII at -300<~V_LSR_<~-150km/s toward all three sightlines at R<~0.2R_vir_, 3 of 4 sightlines at 0.8<~R/R_vir_<~1.1, and possibly 1 of 11 at 1.1<R/R_vir_<~1.8. We present several arguments that the gas at these velocities observed in these directions originates from the M31 CGM rather than the Local Group or Milky Way CGM or Magellanic Stream. We show that the dwarf galaxies located in the CGM of M31 have very similar velocities over similar projected distances from M31. We find a non-trivial relationship only at these velocities between the column densities (N) of all the ions and R, whereby N decreases with increasing R. At R<0.8R_vir_, the covering fraction is close to unity for Si III and C IV (f_c_~60%-97% at the 90% confidence level), but drops to f_c_<~10%-20% at R>~R_vir_. We show that the M31 CGM gas is bound, multiphase, predominantly ionized, and is more highly ionized gas at larger R. We estimate using Si II, Si III, and Si IV, a CGM metal mass of >~2x10^6^M_{sun}_ and gas mass of >~3x10^9^(Z_{sun}_/Z)M_{sun}_ within 0.2R_vir_, and possibly a factor of ~10 larger within R_vir_, implying substantial metal and gas masses in the CGM of M31.
185. HST/COS observations of 7 white dwarfs
ID:
ivo://CDS.VizieR/J/ApJ/823/49
Title:
HST/COS observations of 7 white dwarfs
Short Name:
J/ApJ/823/49
Date:
21 Oct 2021
Publisher:
CDS
Description:
The search for transiting habitable exoplanets has broadened to include several types of stars that are smaller than the Sun in an attempt to increase the observed transit depth and hence the atmospheric signal of the planet. Of all spectral types, white dwarfs (WDs) are the most favorable for this type of investigation. The fraction of WDs that possess close-in rocky planets is unknown, but several large angle stellar surveys have the photometric precision and cadence to discover at least one if they are common. Ultraviolet observations of WDs may allow for detection of molecular oxygen or ozone in the atmosphere of a terrestrial planet. We use archival Hubble Space Telescope data from the Cosmic Origins Spectrograph to search for transiting rocky planets around UV-bright WDs. In the process, we discovered unusual variability in the pulsating WD GD 133, which shows slow sinusoidal variations in the UV. While we detect no planets around our small sample of targets, we do place stringent limits on the possibility of transiting planets, down to sub-lunar radii. We also point out that non-transiting small planets in thermal equilibrium are detectable around hotter WDs through infrared excesses, and identify two candidates.
186. HST/COS obs. of QSO outflows in 500-1050{AA}. VII.
ID:
ivo://CDS.VizieR/J/ApJS/249/15
Title:
HST/COS obs. of QSO outflows in 500-1050{AA}. VII.
Short Name:
J/ApJS/249/15
Date:
21 Oct 2021
Publisher:
CDS
Description:
From Hubble Space Telescope/Cosmic Origins Spectrograph spectra of five quasars, 16 outflows are detected. For 11 outflows, we are able to constrain their distances to the central source (R) and their energetics. In instances of multiple electron number density determinations (used in the calculation of R) for the same outflow, the values are consistent within errors. For the 11 outflows, eight have measurements for R (between 10 and 1000pc), one has a lower limit, another has an upper limit, and the last has a range in R. There are two outflows that have enough kinetic luminosity to be major contributors to active galactic nucleus feedback. The outflowing mass is found primarily in a very high-ionization phase, which is probed using troughs from, e.g., Ne VIII, Na IX, Mg X, and Si XII. Such ions connect the physical conditions of these ultraviolet outflows to the X-ray warm absorber outflows seen in nearby Seyfert galaxies. The ion Cl VII and several new transitions from Ne V have been detected for the first time.
187. HST/COS spectra of QSOs with SiIV data
ID:
ivo://CDS.VizieR/J/ApJ/871/35
Title:
HST/COS spectra of QSOs with SiIV data
Short Name:
J/ApJ/871/35
Date:
21 Oct 2021
Publisher:
CDS
Description:
Every quasar (quasi-stellar object; QSO) spectrum contains absorption-line signatures from the interstellar medium, disk-halo interface, and circumgalactic medium (CGM) of the Milky Way (MW). We analyze Hubble Space Telescope/Cosmic Origins Spectrograph (COS) spectra of 132 QSOs to study the significance and origin of SiIV absorption at |v_LSR_|<=100km/s in the Galactic halo. The gas in the north predominantly falls in at -50<~v_LSR_<~0km/s, whereas in the south, no such pattern is observed. The SiIV column density has an average and a standard deviation of <N_SiIV_>=(3.8+/-1.4)x10^13^cm^-2^. At |b|>~30{deg}, N_SiIV_ does not significantly correlate with b, which cannot be explained by a commonly adopted flat-slab geometry. We propose a two-component model to reconstruct the N_SiIV_-b distribution: a plane-parallel component N_DH_^{perp}^ to account for the MW's disk-halo interface and a global component N_G_ to reproduce the weak dependence on b. We find N_DH_^{perp}^=1.3_-0.7_^+4.7^x10^12^cm^-2^ and N_G_=3.4+/-0.3)x10^13^cm^-2^ on the basis of Bayesian analyses and block bootstrapping. The global component is most likely to have a Galactic origin, although its exact location is uncertain. If it were associated with the MW's CGM, we would find M_gas,all_>~ 4.7x10^9^M_{sun}_(C_f_/1)(R/75kpc)^2^(f_SiIV_/0.3)^-1^(Z/0.3Z_{sun}_)^-1^ for the cool gas at all velocities in the Galactic halo. Our analyses show that there is likely a considerable amount of gas at |v_LSR_|<=100km/s hidden in the MW's CGM.
188. HST -COS & -STIS absorption-line spectroscopy. II.
ID:
ivo://CDS.VizieR/J/ApJS/230/6
Title:
HST -COS & -STIS absorption-line spectroscopy. II.
Short Name:
J/ApJS/230/6
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present basic data and modeling for a survey of the cool, photoionized circumgalactic medium (CGM) of low-redshift galaxies using far-UV QSO absorption-line probes. This survey consists of "targeted" and "serendipitous" CGM subsamples, originally described in Stocke+ (Paper I, 2013ApJ...763..148S). The targeted subsample probes low-luminosity, late-type galaxies at z<0.02 with small impact parameters (<{rho}>=71kpc), and the serendipitous subsample probes higher luminosity galaxies at z<~0.2 with larger impact parameters (<{rho}>=222kpc). Hubble Space Telescope and FUSE UV spectroscopy of the absorbers and basic data for the associated galaxies, derived from ground-based imaging and spectroscopy, are presented. We find broad agreement with the COS-Halos results, but our sample shows no evidence for changing ionization parameter or hydrogen density with distance from the CGM host galaxy, probably because the COS-Halos survey probes the CGM at smaller impact parameters. We find at least two passive galaxies with HI and metal-line absorption, confirming the intriguing COS-Halos result that galaxies sometimes have cool gas halos despite no on-going star formation. Using a new methodology for fitting HI absorption complexes, we confirm the CGM cool gas mass of Paper I, but this value is significantly smaller than that found by the COS-Halos survey. We trace much of this difference to the specific values of the low-z metagalactic ionization rate assumed. After accounting for this difference, a best-value for the CGM cool gas mass is found by combining the results of both surveys to obtain log(M/M_{sun}_)=10.5+/-0.3, or ~30% of the total baryon reservoir of an L>=L^*^, star-forming galaxy.
189. HST/COS survey of z<0.9 AGNs. I.
ID:
ivo://CDS.VizieR/J/ApJ/817/111
Title:
HST/COS survey of z<0.9 AGNs. I.
Short Name:
J/ApJ/817/111
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use high-quality, medium-resolution Hubble Space Telescope/Cosmic Origins Spectrograph (HST/COS) observations of 82 UV-bright active galactic nuclei (AGNs) at redshifts z_AGN_<0.85 to construct the largest survey of the low-redshift intergalactic medium (IGM) to date: 5138 individual extragalactic absorption lines in HI and 25 different metal-ion species grouped into 2611 distinct redshift systems at z_abs_<0.75 covering total redshift pathlengths {Delta}z_HI_=21.7 and {Delta}z_OVI_=14.5. Our semi-automated line-finding and measurement technique renders the catalog as objectively defined as possible. The cumulative column density distribution of HI systems can be parametrized d N(>N)/dz=C_14_(N/10^14^/cm2)^-({beta}-1)^, with C_14_=25+/-1 and {beta}=1.65+/-0.02. This distribution is seen to evolve both in amplitude, C_14_{propto}(1+z)^2.3+/-0.1^, and slope {beta}(z)=1.75-0.31 z for z<=0.47. We observe metal lines in 418 systems, and find that the fraction of IGM absorbers detected in metals is strongly dependent on N_H1_. The distribution of OVI absorbers appears to evolve in the same sense as the Ly{alpha} forest. We calculate contributions to {Omega}_b_ from different components of the low-z IGM and determine the Ly{alpha} decrement as a function of redshift. IGM absorbers are analyzed via a two-point correlation function in velocity space. We find substantial clustering of HI absorbers on scales of {Delta}v=50-300km/s with no significant clustering at {Delta}v>~1000km/s. Splitting the sample into strong and weak absorbers, we see that most of the clustering occurs in strong, N_HI_>~10^13.5^/cm2, metal-bearing IGM systems.
190. HST/COS UV obs. of low-z SDSS galaxy groups
ID:
ivo://CDS.VizieR/J/ApJS/240/15
Title:
HST/COS UV obs. of low-z SDSS galaxy groups
Short Name:
J/ApJS/240/15
Date:
21 Oct 2021
Publisher:
CDS
Description:
A small survey of the UV-absorbing gas in 12 low-z galaxy groups has been conducted using the Cosmic Origins Spectrograph on board the Hubble Space Telescope. Targets were selected from a large, homogeneously selected sample of groups found in the Sloan Digital Sky Survey. A critical selection criterion excluded sight lines that pass close (<1.5 virial radii) to a group galaxy, to ensure absorber association with the group as a whole. Deeper galaxy redshift observations are used both to search for closer galaxies and also to characterize these 10^13.5^-10^14.5^M_{sun}_ groups, the most massive of which are highly virialized with numerous early-type galaxies (ETGs). This sample also includes two spiral-rich groups, not yet fully virialized. At group-centric impact parameters of 0.3-2Mpc, these signal-to-noise ratios = 15-30 spectra detected HI absorption in 7 of 12 groups; high (OVI) and low (SiIII) ion metal lines are present in two-thirds of the absorption components. None of the three most highly virialized, ETG-dominated groups are detected in absorption. Covering fractions >~50% are seen at all impact parameters probed, but do not require large filling factors despite an enormous extent. Unlike halo clouds in individual galaxies, group absorbers have radial velocities that are too low to escape the group potential well without doubt. This suggests that these groups are "closed boxes" for galactic evolution in the current epoch. Evidence is presented that the cool and warm group absorbers are not a pervasive intra-group medium (IGrM), requiring a hotter (T~10^6^-10^7^K) IGrM to be present to close the baryon accounting.