- ID:
- ivo://CDS.VizieR/J/A+A/654/A132
- Title:
- X-shooter spectra of AGN and inactive galaxies
- Short Name:
- J/A+A/654/A132
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The relation between nuclear (<~50pc) star formation and nuclear galactic activity is still elusive; theoretical models predict a link between the two, but it is unclear whether active galactic nuclei (AGNs) should appear at the same time, before, or after nuclear star formation activity. We present a study of this relation in a complete, volume-limited sample of nine of the most luminous (log_L14-195keV_>10^42.5^erg/s) local AGNs (the LLAMA sample), including a sample of 18 inactive control galaxies (six star-forming; 12 passive) that are matched by Hubble type, stellar mass (9.5<~logM*/M_{sun}_<~10.5), inclination, and distance. This allows us to calibrate our methods on the control sample and perform a differential analysis between the AGN and control samples. We performed stellar population synthesis on VLT/X-shooter spectra in an aperture corresponding to a physical radius of ~150pc. We find young (<~30Myr) stellar populations in seven out of nine AGNs and in four out of six star-forming control galaxies. In the non-star-forming control population, in contrast, only two out of 12 galaxies show such a population. We further show that these young populations are not indicative of ongoing star formation, providing evidence for models that see AGN activity as a consequence of nuclear star formation. Based on the similar nuclear star formation histories of AGNs and star-forming control galaxies, we speculate that the latter may turn into the former for some fraction of their time. Under this assumption, and making use of the volume completeness of our sample, we infer that the AGN phase lasts for about 5% of the nuclear starburst phase.
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- ID:
- ivo://CDS.VizieR/J/A+A/628/A61
- Title:
- X-shooter spectra of 43 metal-poor M dwarfs
- Short Name:
- J/A+A/628/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of the project is to define metallicity/gravity/temperature scales for different spectral types of metal-poor M dwarfs. We obtained intermediate-resolution ultraviolet (UVB), optical (VIS), and near-infrared (NIR) spectra of 43 metal-poor M dwarfs (16 sdMs, 16 esdMs, and 12 usdMs with the ESO VLT X-shooter spectrograph. We compared our atlas of spectra to the BT-Settl synthetic spectral energy distribution over a wide range of metallicities, gravities, and effective temperatures to infer the physical properties for the whole M dwarf sequence at sub-solar metallicities and constrain the latest atmospheric models. The BT-Settl models accurately reproduce the observed spectra across the 450--2500 nm wavelength range except for a few regions. We find that the best fits for gravities of log(g)=5.0-5.5 for the three metal classes. We infer metallicities of [Fe/H]=-0.5, -1.5, and -2.0+/-0.5dex and effective temperatures of 3700-2600K, 3800-2900K, and 3700-2900K for sdMs, esdMs, and usdMs, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A1
- Title:
- X-shooter spectra of 6 ~2.2 quasars
- Short Name:
- J/A+A/603/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We studied the spectra of six z~2.2 quasars obtained with the X-shooter spectrograph at the Very Large Telescope. The redshift of these sources and X-shooter's spectral coverage allow us to cover the rest spectral range ~1200-7000{AA} for the simultaneous detection of optical and ultraviolet lines emitted by the Broad Line Region. Simultaneous measurements, avoiding issues related to quasars variability, help us understanding the connection between different Broad Line Region line profiles generally used as virial estimators of Black Holes masses in quasars. The goal of this work is comparing the emission lines from the same object to check on the reliability of H{alpha}, MgII and CIV with respect to H{beta}. H{alpha} and MgII linewidths correlate well with H{beta}, while CIV shows a poorer correlation, due to the presence of strong blueshifts and asymmetries in the profile. We compare our sample with the only other two whose spectra were taken with the same instrument and for all examined lines our results are in agreement with the ones obtained with X-shooter at z~1.5-1.7. We finally evaluate CIII] as a possible substitute of CIV in the same spectral range and find that its behaviour is more coherent with those of the other lines: we believe that, when a high quality spectrum such as the ones we present is available and a proper modelization with the FeII and FeIII emissions is performed, the use of this line is more appropriate than that of CIV if not corrected for the contamination by non-virialized components.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/538
- Title:
- XUV-Disk galaxies in the Local Universe
- Short Name:
- J/ApJS/173/538
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have initiated a search for extended ultraviolet disk (XUV-disk) galaxies in the local universe. Here we compare GALEX UV and visible-NIR images of 189 nearby (D<40Mpc) S0-Sm galaxies included in the GALEX Atlas of Nearby Galaxies (Gil de Paz et al. 2007, Cat. J/ApJS/173/185) and present the first catalog of XUV-disk galaxies. We find that XUV-disk galaxies are surprisingly common but have varied relative (UV/optical) extent and morphology. Type 1 objects (>~20% incidence) have structured, UV-bright/optically faint emission features in the outer disk, beyond the traditional star formation threshold. Type 2 XUV-disk galaxies (~10% incidence) exhibit an exceptionally large, UV-bright/optically low surface brightness (LSB) zone having blue UV-K_s_ outside the effective extent of the inner, older stellar population, but not reaching extreme galactocentric distance.
- ID:
- ivo://CDS.VizieR/J/ApJS/222/6
- Title:
- 4.5yr obs. of Mrk421 with ARGO-YBJ & Fermi
- Short Name:
- J/ApJS/222/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the extensive multi-wavelength observations of the blazar Markarian 421 (Mrk 421) covering radio to {gamma}-rays, during the 4.5yr period of ARGO-YBJ and Fermi common operation time, from 2008 August to 2013 February. These long-term observations, extending over an energy range of 18 orders of magnitude, provide a unique chance to study the variable emission of Mrk 421. In particular, due to the ARGO-YBJ and Fermi data, the entire energy range from 100MeV to 10TeV is covered without any gap. In the observation period, Mrk 421 showed both low- and high-activity states at all wavebands. The correlations among flux variations in different wavebands were analyzed. The X-ray flux is clearly correlated with the TeV {gamma}-ray flux, while the GeV {gamma}-rays only show a partial correlation with the TeV {gamma}-rays. Radio and UV fluxes seem to be weakly or not correlated with the X-ray and {gamma}-ray fluxes. Seven large flares, including five X-ray flares and two GeV {gamma}-ray flares with variable durations (3-58d), and one X-ray outburst phase were identified and used to investigate the variation of the spectral energy distribution with respect to a relative quiescent phase. During the outburst phase and the seven flaring episodes, the peak energy in X-rays is observed to increase from sub-keV to a few keV. The TeV {gamma}-ray flux increases up to 0.9-7.2 times the flux of the Crab Nebula. The behavior of GeV {gamma}-rays is found to vary depending on the flare, a feature that leads us to classify flares into three groups according to the GeV flux variation. Finally, the one-zone synchrotron self-Compton model was adopted to describe the emission spectra. Two out of three groups can be satisfactorily described using injected electrons with a power-law spectral index around 2.2, as expected from relativistic diffuse shock acceleration, whereas the remaining group requires a harder injected spectrum. The underlying physical mechanisms responsible for different groups may be related to the acceleration process or to the environment properties.
- ID:
- ivo://CDS.VizieR/J/ApJ/891/170
- Title:
- 10yr of radio-to-gamma-ray obs. of 1ES 1215+30.3
- Short Name:
- J/ApJ/891/170
- Date:
- 19 Jan 2022 09:02:08
- Publisher:
- CDS
- Description:
- Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multiwavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100MeV to 30TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline, and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by Very Long Baseline Array at 43.1, 22.2, and 15.3GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed.
- ID:
- ivo://CDS.VizieR/J/ApJ/848/103
- Title:
- ~1.5yr Swift observations of Mrk 421
- Short Name:
- J/ApJ/848/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the Swift observations of the nearby BL Lac object Mrk421 during 2013 November-2015 June. The source exhibited a strong long-term variability in the 0.3-10keV band, with a maximum-to-minimum flux ratio of 13, and underwent X-ray flares by a factor of 1.8-5.2 on timescales of a few weeks or shorter. The source showed 48 instances of intraday flux variability in this period, which sometimes was observed within the 1 ks observational run. It was characterized by fractional amplitudes of 1.5(0.3)%-38.6(0.4)% and flux doubling/halving times of 2.6-20.1hr. The X-ray flux showed a lack of correlation with the TeV flux on some occasions (strong TeV flares were not accompanied by comparable X-ray activity and vice versa), indicating that the high-energy emission in Mrk421 was generated from an emission region more complex than a single zone. The best fits of the 0.3-10keV spectra were mainly obtained using the log-parabola model, showing a strong spectral variability that generally followed a "harder-when-brighter" trend. The position of the synchrotron spectral energy distribution peak showed an extreme range from a few eV to ~10keV that happens rarely in blazars.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/91
- Title:
- z<0.16 CIV absorbers from HST/COS QSOs spectra
- Short Name:
- J/ApJ/815/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To investigate the evolution of metal-enriched gas over recent cosmic epochs as well as to characterize the diffuse, ionized, metal-enriched circumgalactic medium, we have conducted a blind survey for CIV absorption systems in 89 QSO sightlines observed with the Hubble Space Telescope Cosmic Origins Spectrograph. We have identified 42 absorbers at z<0.16, comprising the largest uniform blind sample size to date in this redshift range. Our measurements indicate an increasing CIV absorber number density per comoving path length (dN/dX=7.5+/-1.1) and modestly increasing mass density relative to the critical density of the universe ({Omega}_CIV_=10.0+/-1.5x10^-8^) from z~1.5 to the present epoch, consistent with predictions from cosmological hydrodynamical simulations. Furthermore, the data support a functional form for the column density distribution function that deviates from a single power law, also consistent with independent theoretical predictions. As the data also probe heavy element ions in addition to CIV at the same redshifts, we identify, measure, and search for correlations between column densities of these species where components appear to be aligned in velocity. Among these ion-ion correlations, we find evidence for tight correlations between CII and SiII, CII and SiIII, and CIV and SiIV, suggesting that these pairs of species arise in similar ionization conditions. However, the evidence for correlations decreases as the difference in ionization potential increases. Finally, when controlling for observational bias, we find only marginal evidence for a correlation (86.8% likelihood) between the Doppler line width b(CIV) and column density N(CIV).
- ID:
- ivo://CDS.VizieR/J/MNRAS/457/629
- Title:
- ZFOURGE catalogue of AGN candidates
- Short Name:
- J/MNRAS/457/629
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate active galactic nuclei (AGN) candidates within the FourStar Galaxy Evolution Survey (ZFOURGE) to determine the impact they have on star formation in their host galaxies. We first identify a population of radio, X-ray, and infrared-selected AGN by cross-matching the deep Ks-band imaging of ZFOURGE with overlapping multiwavelength data. From this, we construct a mass-complete (log(M*/M_{sun}_)>=9.75), AGN luminosity limited sample of 235 AGN hosts over z=0.2-3.2. We compare the rest-frame U-V versus V-J (UVJ) colours and specific star formation rates (sSFRs) of the AGN hosts to a mass-matched control sample of inactive (non-AGN) galaxies. UVJ diagnostics reveal AGN tend to be hosted in a lower fraction of quiescent galaxies and a higher fraction of dusty galaxies than the control sample. Using 160{mu}m Herschel PACS data, we find the mean specific star formation rate of AGN hosts to be elevated by 0.34-/-0.07dex with respect to the control sample across all redshifts. This offset is primarily driven by infrared-selected AGN, where the mean sSFR is found to be elevated by as much as a factor of ~5. The remaining population, comprised predominantly of X-ray AGN hosts, is found mostly consistent with inactive galaxies, exhibiting only a marginal elevation. We discuss scenarios that may explain these findings and postulate that AGN are less likely to be a dominant mechanism for moderating galaxy growth via quenching than has previously been suggested.
- ID:
- ivo://CDS.VizieR/J/ApJ/653/53
- Title:
- z~6 galaxies UV luminosity function
- Short Name:
- J/ApJ/653/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have detected 506 i-dropouts (z~6 galaxies) in deep, wide-area HST ACS fields: HUDF, enhanced GOODS, and HUDF parallel ACS fields (HUDF-Ps). The contamination levels are <~8% (i.e., >~92% are at z~6). With these samples, we present the most comprehensive, quantitative analyses of z~6 galaxies yet and provide optimal measures of the UV luminosity function (LF) and luminosity density at z~6, and their evolution to z~3. We redetermine the size and color evolution from z~6 to z~3. Field-to-field variations (cosmic variance), completeness, flux, and contamination corrections are modeled systematically and quantitatively.
