18 research outputs found
The signature of dissipation in the mass-size relation: are bulges simply spheroids wrapped in a disc?
The relation between the stellar mass and size of a galaxy's structural
subcomponents, such as discs and spheroids, is a powerful way to understand the
processes involved in their formation. Using very large catalogues of
photometric bulge+disc structural decompositions and stellar masses from the
Sloan Digital Sky Survey Data Release Seven, we carefully define two large
subsamples of spheroids in a quantitative manner such that both samples share
similar characteristics with one important exception: the 'bulges' are embedded
in a disc and the 'pure spheroids' are galaxies with a single structural
component. Our bulge and pure spheroid subsample sizes are 76,012 and 171,243
respectively. Above a stellar mass of ~ M, the mass-size
relations of both subsamples are parallel to one another and are close to lines
of constant surface mass density. However, the relations are offset by a factor
of 1.4, which may be explained by the dominance of dissipation in their
formation processes. Whereas the size-mass relation of bulges in discs is
consistent with gas-rich mergers, pure spheroids appear to have been formed via
a combination of 'dry' and 'wet' mergers.Comment: Accepted for publication in MNRAS, 6 pages, 3 figure
The chemistry of the most metal-rich damped Lyman α systems at z∼2 - II. Context with the Local Group
Using our sample of the most metal-rich damped Lyman α systems (DLAs) at zabs∼2, and two literature compilations of chemical abundances in 341 DLAs and 2818 stars, we present an analysis of the chemical composition of DLAs in the context of the Local Group. The metal-rich sample of DLAs at zabs∼2 probes metallicities as high as the Galactic disc and the most metal-rich dwarf spheroidals (dSphs), permitting an analysis of many elements typically observed in DLAs (Fe, Zn, Cr, Mn, Si, and S) in comparison to stellar abundances observed in the Galaxy and its satellites (in particular dSphs). Our main conclusions are: (1) non-solar [Zn/Fe] abundances in metal-poor Galactic stars and in dSphs over the full metallicity range probed by DLAs, suggest that Zn is not a simple proxy for Fe in DLAs and therefore not a suitable indicator of dust depletion. After correcting for dust depletion, the majority of DLAs have subsolar [Zn/Fe] similar to dSphs; (2) at [Fe/H]∼−0.5, a constant [Mn/Fe]∼−0.5 and near-solar [α/Fe] (requiring an assumption about dust depletion) are in better agreement with dwarf galaxies than Galactic disc stars; (3) [α/Zn] is usually solar or subsolar in DLAs. However, although low ratios of [α/Fe] are usually considered more ‘dwarf-like' than ‘Milky Way-like', subsolar [Zn/Fe] in Local Group dwarfs leads to supersolar [α/Zn] in the dSphs, in contrast with the DLAs. Therefore, whilst DLAs exhibit some similarities with the Local Group dwarf population, there are also notable difference
The COS-AGN survey: Revealing the nature of circum-galactic gas around hosts of active galactic nuclei
Active galactic nuclei (AGN) are thought to play a critical role in shaping
galaxies, but their effect on the circumgalactic medium (CGM) is not well
studied. We present results from the COS-AGN survey: 19 quasar sightlines that
probe the CGM of 20 optically-selected AGN host galaxies with impact parameters
kpc. Absorption lines from a variety of species are
measured and compared to a stellar mass and impact parameter matched sample of
sightlines through non-AGN galaxies. Amongst the observed species in the
COS-AGN sample (HI, CII, SiII, SiIII, CIV, SiIV, NV), only Ly shows a
high covering fraction (% for rest-frame equivalent widths EW m\AA) whilst many of the metal ions are not detected in individual
sightlines. A sightline-by-sightline comparison between COS-AGN and the control
sample yields no significant difference in EW distribution. However, stacked
spectra of the COS-AGN and control samples show significant (> 3 sigma)
enhancements in the EW of both Ly and SiIII at impact parameters kpc by a factor of dex and dex respectively. The
lack of detections of both high-ionization species near the AGN and strong
kinematic offsets between the absorption systemic galaxy redshifts indicates
that neither the AGN's ionization nor its outflows are the origin of these
differences. Instead, we suggest the observed differences could result from
either AGN hosts residing in haloes with intrinsically distinct gas properties,
or that their CGM has been affected by a previous event, such as a starburst,
which may also have fuelled the nuclear activity.Comment: Accepted for publication in MNRA
SPLUS J142445.34-254247.1: An R-Process Enhanced, Actinide-Boost, Extremely Metal-Poor star observed with GHOST
We report on the chemo-dynamical analysis of SPLUS J142445.34-254247.1, an
extremely metal-poor halo star enhanced in elements formed by the rapid
neutron-capture process. This star was first selected as a metal-poor candidate
from its narrow-band S-PLUS photometry and followed up spectroscopically in
medium-resolution with Gemini South/GMOS, which confirmed its low-metallicity
status. High-resolution spectroscopy was gathered with GHOST at Gemini South,
allowing for the determination of chemical abundances for 36 elements, from
carbon to thorium. At [Fe/H]=-3.39, SPLUS J1424-2542 is one of the lowest
metallicity stars with measured Th and has the highest logeps(Th/Eu) observed
to date, making it part of the "actinide-boost" category of r-process enhanced
stars. The analysis presented here suggests that the gas cloud from which SPLUS
J1424-2542 was formed must have been enriched by at least two progenitor
populations. The light-element (Z<=30) abundance pattern is consistent with the
yields from a supernova explosion of metal-free stars with 11.3-13.4 Msun, and
the heavy-element (Z>=38) abundance pattern can be reproduced by the yields
from a neutron star merger (1.66Msun and 1.27Msun) event. A kinematical
analysis also reveals that SPLUS J1424-2542 is a low-mass, old halo star with a
likely in-situ origin, not associated with any known early merger events in the
Milky Way.Comment: 26 pages, 11 figures, accepted for publication on Ap
Performance of ESPRESSO’S high-resolution 4 × 2 binning for characterising intervening absorbers towards faint quasars
As of October 2021 (Period 108), the European Southern Observatory (ESO) offers a new mode of the ESPRESSO spectrograph designed to use the high-resolution grating with 4 × 2 binning (spatial by spectral; HR42 mode), with the specific objective of observing faint targets with a single Unit Telescope at Paranal. We validated the new HR42 mode using four hours of on-target observations of the quasar J0003-2603, known to host an intervening metal-poor absorber along the line of sight. The capabilities of the ESPRESSO HR42 mode (resolving power R ≈ 137 000) were evaluated by comparing them to a UVES spectrum of the same target with a similar integration time but lower resolving power (R ≈ 48 000). For both data sets, we tested the ability to decompose the velocity profile of the intervening absorber using Voigt profile fitting and extracted the total column densities of C I
Evidence of First Stars-enriched Gas in High-redshift Absorbers
The first stars were born from chemically pristine gas. They were likely massive, and thus they rapidly exploded as supernovae, enriching the surrounding gas with the first heavy elements. In the Local Group, the chemical signatures of the first stellar population were identified among low-mass, long-lived, very metal-poor ([Fe/H] +0.7): the so-called carbon-enhanced metal-poor stars. Conversely, a similar carbon excess caused by first-star pollution was not found in dense neutral gas traced by absorption systems at different cosmic time. Here we present the detection of 14 very metal-poor, optically thick absorbers at redshift z ∼ 3–4. Among these, 3 are carbon-enhanced and reveal an overabundance with respect to Fe of all the analyzed chemical elements (O, Mg, Al, and Si). Their relative abundances show a distribution with respect to [Fe/H] that is in very good agreement with those observed in nearby very metal-poor stars. All the tests we performed support the idea that these C-rich absorbers preserve the chemical yields of the first stars. Our new findings suggest that the first-star signatures can survive in optically thick but relatively diffuse absorbers, which are not sufficiently dense to sustain star formation and hence are not dominated by the chemical products of normal stars
Sub-damped Lyman alpha systems in the XQ-100 survey - I. Identification and contribution to the cosmological H I budget
Sub-damped Lyman alpha systems (subDLAs; HI column densities of
19.0<=logN(HI)<20.3) are rarely included in the cosmic HI census performed at
redshifts z>=1.5, yet are expected to contribute significantly to the overall
HI mass budget of the Universe. In this paper, we present a blindly selected
sample of 155 subDLAs found along 100 quasar sightlines (with a redshift path
length X=475) in the XQ-100 survey to investigate the contribution of subDLAs
to the HI mass density of the Universe. The impact of X-Shooter's spectral
resolution on sub-DLA identification is evaluated, and found to be sufficient
for reliably finding absorbers with logN(HI)>=18.9. We compared the
implications of searching for subDLAs solely using HI absorption versus the use
of additional metal lines to confirm the identification, and found that
metal-selection techniques would have missed 75 subDLAs. Using a
bootstrap-Monte Carlo simulation, we computed the column density distribution
function (f(N,X)) and the cosmological HI mass density of subDLAs and compared
with our previous work based on the XQ-100 damped Lyman alpha systems. We do
not find any significant redshift evolution in f(N,X) or cosmological HI mass
density for subDLAs. However, subDLAs contribute 10-20 per cent of the total
cosmological HI mass density measured at redshifts 2<z<5 (agreeing with
previous measurements), and thus have a small but significant contribution to
the HI budget of the Universe.Comment: Accepted for publication in MNRAS. 55 pages (41 pages of appendix
containing subDLA catalogue and evolution curves