41 research outputs found
Probing galaxy evolution through HI 21-cm emission and absorption: current status and prospects with the Square Kilometre Array
One of the major science goals of the Square Kilometre Array (SKA) is to
understand the role played by atomic hydrogen (HI) gas in the evolution of
galaxies throughout cosmic time. The hyperfine transition line of the hydrogen
atom at 21-cm is one of the best tools to detect and study the properties of HI
gas associated with galaxies. In this article, we review our current
understanding of HI gas and its relationship with galaxies through observations
of the 21-cm line both in emission and absorption. In addition, we provide an
overview of the HI science that will be possible with SKA and its pre-cursors
and pathfinders, i.e. HI 21-cm emission and absorption studies of galaxies from
nearby to high redshifts that will trace various processes governing galaxy
evolution.Comment: 31 pages, 7 figures, accepted on 27 May 2022 for publication in the
Journal of Astrophysics and Astronomy (to appear in the special issue on
"Indian participation in the SKA"), figure 4 has been update
MUSE Analysis of Gas around Galaxies (MAGG) -- V: Linking ionized gas traced by CIV and SiIV absorbers to Ly emitting galaxies at
We use 28 quasar fields with high-resolution (HIRES and UVES) spectroscopy
from the MUSE Analysis of Gas Around Galaxies survey to study the connection
between Ly emitters (LAEs) and metal-enriched ionized gas traced by
CIV in absorption at redshift . In a sample of 220 CIV absorbers,
we identify 143 LAEs connected to CIV gas within a line-of-sight separation
, equal to a detection rate of per cent
once we account for multiple LAEs connected to the same CIV absorber. The
luminosity function of LAEs associated with CIV absorbers shows a
higher normalization factor compared to the field. CIV with higher equivalent
width and velocity width are associated with brighter LAEs or multiple
galaxies, while weaker systems are less often identified near LAEs. The
covering fraction in groups is up to times larger than for isolated
galaxies. Compared to the correlation between optically-thick HI absorbers and
LAEs, CIV systems are twice less likely to be found near LAEs especially at
lower equivalent width. Similar results are found using SiIV as tracer of
ionized gas. We propose three components to model the gas environment of LAEs:
i) the circumgalactic medium of galaxies, accounting for the strongest
correlations between absorption and emission; ii) overdense gas filaments
connecting galaxies, driving the excess of LAEs at a few times the virial
radius and the modulation of the luminosity and cross-correlation functions for
strong absorbers; iii) an enriched and more diffuse medium, accounting for
weaker CIV absorbers farther from galaxies.Comment: 28 pages, 21 figures, 10 tables. Submitted to MNRAS after accounting
for reviewer's comment
Constraining the Size of the Circumgalactic Medium Using the Transverse Autocorrelation Function of C IV Absorbers in Paired Quasar Spectra
The circumgalactic medium (CGM) plays a vital role in the formation and
evolution of galaxies, acting as a lifeline between galaxies and the
surrounding intergalactic medium (IGM). In this study we leverage a unique
sample of quasar pairs to investigate the properties of the CGM with absorption
line tomography. We present a new sample of medium resolution Keck/ESI,
Magellan/MagE, and VLT/XSHOOTER spectra of 29 quasar pairs at redshift . We supplement the sample with additional spectra of 32 pairs from the
literature, creating a catalog of 61 quasar pairs with angular separations
between 1.7" and 132.9" and projected physical separations () between
14 kpc and 887 kpc. We construct a catalog of 906 metal-line absorption
doublets of C IV () with equivalent widths ranging
from 6 m{\AA} m{\AA}. The best fit linear model to
the log-space equivalent width frequency distribution () of the sample yields coefficients of and
. To constrain the projected extent of C IV, we calculate the
transverse autocorrelation function. The flattening of the autocorrelation
function at low provides a lower limit for the coherence length of
the metal enriched CGM - on the order of 200 comoving kpc. This
physical size constraint allows us to refine our understanding of the metals in
the CGM, where the extent of C IV in the CGM depends on gas flows, feedback,
timescale of metal injection and mixing, and the mass of the host galaxies.Comment: 19 pages, 8 figures, 2 tables, Accepted for publication by The
Astronomical Journa
Metal line emission from galaxy haloes at z~1
We present a study of the metal-enriched halo gas, traced using MgII and
[OII] emission lines, in two large, blind galaxy surveys - the MUSE (Multi Unit
Spectroscopic Explorer) Analysis of Gas around Galaxies (MAGG) and the MUSE
Ultra Deep Field (MUDF). By stacking a sample of ~600 galaxies (stellar masses
M* ~10^{6-12} Msun), we characterize for the first time the average metal line
emission from a general population of galaxy haloes at 0.7 <= z <= 1.5. The
MgII and [OII] line emission extends farther out than the stellar continuum
emission, on average out to ~25 kpc and ~45 kpc, respectively, at a surface
brightness (SB) level of 10^{-20} erg/s/cm2/arcsec2. The radial profile of the
MgII SB is shallower than that of the [OII], suggesting that the resonant MgII
emission is affected by dust and radiative transfer effects. The [OII] to MgII
SB ratio is ~3 over ~20-40 kpc, also indicating a significant in situ origin of
the extended metal emission. The average SB profiles are intrinsically brighter
by a factor ~2-3 and more radially extended by a factor of ~1.3 at 1.0 < z <=
1.5 than at 0.7 <= z <= 1.0. The average extent of the metal emission also
increases independently with increasing stellar mass and in overdense group
environments. When considering individual detections, we find extended [OII]
emission up to ~50 kpc around ~30-40 percent of the group galaxies, and
extended (~30-40 kpc) MgII emission around two z~1 quasars in groups, which
could arise from outflows or environmental processes.Comment: 24 pages, 21 figures, 2 tables, accepted for publication in MNRA
ALMACAL VI: Molecular gas mass density across cosmic time via a blind search for intervening molecular absorbers
We are just starting to understand the physical processes driving the dramatic change in cosmic star-formation rate between z ⌠2 and the present day. A quantity directly linked to star formation is the molecular gas density, which should be measured through independent methods to explore variations due to cosmic variance and systematic uncertainties. We use intervening CO absorption lines in the spectra of mm-bright background sources to provide a census of the molecular gas mass density of the Universe. The data used in this work are taken from ALMACAL, a wide and deep survey utilizing the ALMA calibrator archive. While we report multiple Galactic absorption lines and one intrinsic absorber, no extragalactic intervening molecular absorbers are detected. However, thanks to the large redshift path surveyed (Îz = 182), we provide constraints on the molecular column density distribution function beyond z ⌠0. In addition, we probe column densities of N(H2) > 1016 atoms cmâ2, five orders of magnitude lower than in previous studies. We use the cosmological hydrodynamical simulation IllustrisTNG to show that our upper limits of Ï(H2) âČ 108.3MâMpcâ3 at 0 < z †1.7 already provide new constraints on current theoretical predictions of the cold molecular phase of the gas. These results are in agreement with recent CO emission-line surveys and are complementary to those studies. The combined constraints indicate that the present decrease of the cosmic star-formation rate history is consistent with an increasing depletion of molecular gas in galaxies compared to z ⌠2