Galaxies are thought to be fed by the continuous accretion of intergalactic gas, but direct observational evidence has been elusive. The accreted gas is expected to orbit about the galaxy's halo, ...delivering not just fuel for star formation but also angular momentum to the galaxy, leading to distinct kinematic signatures. We report observations showing these distinct signatures near a typical distant star-forming galaxy, where the gas is detected using a background quasar passing 26 kiloparsecs from the host. Our observations indicate that gas accretion plays a major role in galaxy growth because the estimated accretion rate is comparable to the star-formation rate.
Spatially resolved metal gas clouds Péroux, C; Rahmani, H; Arrigoni Battaia, F ...
Monthly notices of the Royal Astronomical Society. Letters,
09/2018, Volume:
479, Issue:
1
Journal Article
Peer reviewed
Open access
ABSTRACT We now have mounting evidences that the circumgalactic medium (CGM) of galaxies is polluted with metals processed through stars. The fate of these metals is however still an open question ...and several findings indicate that they remain poorly mixed. A powerful tool to study the low-density gas of the CGM is offered by absorption lines in quasar spectra, although the information retrieved is limited to 1D along the sightline. We report the serendipitous discovery of two close-by bright zgal = 1.148 extended galaxies with a fortuitous intervening zabs = 1.067 foreground absorber. MUSE IFU observations spatially probes kpc-scales in absorption in the plane of the sky over a total area spanning ∼30 kpc−2. We identify two O ii emitters at zabs down to 21 kpc with SFR ∼ 2 M⊙ yr−1. We measure small fractional variations (<30 per cent) in the equivalent widths of Fe ii and Mg ii cold gas absorbers on coherence scales of 8 kpc but stronger variation on larger scales (25 kpc). We compute the corresponding cloud gas mass <2 × 109 M⊙. Our results indicate a good efficiency of the metal mixing on kpc-scales in the CGM of a typical z ∼ 1 galaxy. This study show-cases new prospects for mapping the distribution and sizes of metal clouds observed in absorption against extended background sources with 3D spectroscopy.
The circumgalactic medium (CGM) can be probed through the analysis of absorbing systems in the line of sight to bright background quasars. We present measurements of the metallicity of a new sample ...of 15 sub-damped Lyman α absorbers (sub-DLAs, defined as absorbers with 19.0 < log N(H I) < 20.3) with redshift 0.584 ≤ z
abs ≤ 3.104 from the ESO Ultra-Violet Echelle Spectrograph (UVES) Advanced Data Products Quasar Sample (EUADP). We combine these results with other measurements from the literature to produce a compilation of metallicity measurements for 92 sub-DLAs as well as a sample of 362 DLAs. We apply a multi-element analysis to quantify the amount of dust in these two classes of systems. We find that either the element depletion patterns in these systems differ from the Galactic depletion patterns or they have a different nucleosynthetic history than our own Galaxy. We propose a new method to derive the velocity width of absorption profiles, using the modelled Voigt profile features. The correlation between the velocity width ΔV
90 of the absorption profile and the metallicity is found to be tighter for DLAs than for sub-DLAs. We report hints of a bimodal distribution in the Fe/H metallicity of low redshift (z < 1.25) sub-DLAs, which is unseen at higher redshifts. This feature can be interpreted as a signature from the metal-poor, accreting gas and the metal-rich, outflowing gas, both being traced by sub-DLAs at low redshifts.
ABSTRACT
The existence of a spatially resolved star-forming main sequence (rSFMS) and a spatially resolved mass–metallicity relation (rMZR) is now well established for local galaxies. Moreover, ...gradients with metallicity decreasing with radius seem to be common in local disc galaxies. These observations suggest that galaxy formation is a self-regulating process, and provide constraints for galaxy evolution models. Studying the evolution of these relations at higher redshifts is still, however, very challenging. In this paper, we analyse three gravitationally lensed galaxies at z = 0.6, 0.7, and 1, observed with MUSE and SINFONI. These galaxies are highly magnified by galaxy clusters, which allow us to observe resolved scaling relations and metallicity gradients on physical scales of a couple of hundred parsecs, comparable to studies of local galaxies. We confirm that the rSFMS is already in place at these redshifts on sub-kpc scales, and establish, for the first time, the existence of the rMZR at higher redshifts. We develop a forward-modelling approach to fit 2D metallicity gradients of multiply imaged lensed galaxies in the image plane, and derive gradients of −0.027 ± 0.003, −0.019 ± 0.003, and −0.039 ± 0.060 dex kpc−1. Despite the fact that these are clumpy galaxies, typical of high-redshift discs, the metallicity variations in the galaxies are well described by global linear gradients, and we do not see any difference in metallicity associated with the star-forming clumps.
ABSTRACT
We use a background quasar to detect the presence of circumgalactic gas around a
low-mass star-forming galaxy. Data from the new Multi Unit Spectroscopic Explorer (MUSE) on the Very Large ...Telescope show that the galaxy has a dust-corrected star formation rate (SFR) of 4.7 ± 2.0
M
⊙
yr
−1
, with no companion down to 0.22
M
⊙
yr
−1
(5
σ
) within 240
kpc (“30”). Using a high-resolution spectrum of the background quasar, which is fortuitously aligned with the galaxy major axis (with an azimuth angle
α
of only 15°), we find, in the gas kinematics traced by low-ionization lines, distinct signatures consistent with those expected for a “cold-flow disk” extending at least 12 kpc (
). We estimate the mass accretion rate
to be at least two to three times larger than the SFR, using the geometric constraints from the IFU data and the H
i
column density of log
/
≃ 20.4 obtained from a
Hubble Space Telescope
/COS near-UV spectrum. From a detailed analysis of the low-ionization lines (e.g., Zn
ii
, Cr
ii
, Ti
ii
, Mn
ii
, Si
ii
), the accreting material appears to be enriched to about 0.4
(albeit with large uncertainties:
), which is comparable to the galaxy metallicity (12 + log O/H = 8.7 ± 0.2), implying a large recycling fraction from past outflows. Blueshifted Mg
ii
and Fe
ii
absorptions in the galaxy spectrum from the MUSE data reveal the presence of an outflow. The Mg
ii
and Fe
ii
absorption line ratios indicate emission infilling due to scattering processes, but the MUSE data do not show any signs of fluorescent Fe
ii
* emission.
ABSTRACT
The distribution of gas and metals in the circumgalactic medium (CGM) plays a critical role in how galaxies evolve. The MUSE-ALMA Haloes survey combines MUSE, ALMA, and HST observations to ...constrain the properties of the multiphase gas in the CGM and the galaxies associated with the gas probed in absorption. In this paper, we analyse the properties of galaxies associated with 32 strong ${\rm H\, {\small I}}$ Ly-α absorbers at redshift 0.2 ≲ z ≲ 1.4. We detect 79 galaxies within ±500 kms−1 of the absorbers in our 19 MUSE fields. These associated galaxies are found at physical distances from 5.7 kpc and reach star formation rates as low as 0.1 M⊙ yr−1. The significant number of associated galaxies allows us to map their physical distribution on the Δv and b plane. Building on previous studies, we examine the physical and nebular properties of these associated galaxies and find the following: (i) 27/32 absorbers have galaxy counterparts and more than 50 per cent of the absorbers have two or more associated galaxies, (ii) the ${\rm H\, {\small I}}$ column density of absorbers is anticorrelated with the impact parameter (scaled by virial radius) of the nearest galaxy as expected from simulations, (iii) the metallicity of associated galaxies is typically larger than the absorber metallicity, which decreases at larger impact parameters. It becomes clear that while strong ${\rm H\, {\small I}}$ absorbers are typically associated with more than a single galaxy, we can use them to statistically map the gas and metal distribution in the CGM.
ABSTRACT Gas-rich galaxies are selected efficiently via quasar absorption lines. Recently, a new perspective on such absorption-selected systems has opened up by studying the molecular gas content of ...absorber host galaxies using ALMA CO emission line observations. Here, we present an analysis of multiple CO transitions ($L^{\prime }_{\rm CO} \sim 10^9$ K km s−1) in two z ∼ 0.5 galaxies associated with one Ly α absorber towards J0238+1636. The CO spectral line energy distributions (CO SLEDs) of these galaxies appear distinct from that of typical star-forming galaxies at similar redshifts and is comparable with that of luminous infrared galaxies or active galactic nucleus (AGN). Indeed, these galaxies are associated with optically identified AGN activity. We infer that the CO line ratios and the αCO conversion factor differ from the Galactic values. Our findings suggest that at least a fraction of absorption-selected systems shows interstellar medium conditions deviating from those of normal star-forming galaxies. For a robust molecular gas mass calculation, it is therefore important to construct the CO SLED. Absorption line selection identifies systems with widely distributed gas, which may preferentially select interacting galaxies, which in turn will have more excited CO SLEDs than isolated galaxies. Furthermore, we raise the question whether quasar absorbers preferentially trace galaxy overdensities.
We searched for evidence of the reddening of background quasi-stellar object (QSO) spectra from the Sloan Digital Sky Survey (SDSS) due to dust in intervening damped Lyman α systems (DLAs). We ...utilize the two Data Releases DR5 and DR7 to arrive at sample sizes of 475 (DR5) and 676 (DR7) absorbers, based on two different published lists of SDSS DLAs. Both samples span roughly the redshift range of 2.2 < zabs < 5.2, with a mean of z∼ 3.0, and the majority of the DLAs (75 per cent) below z= 3.3. We construct geometric mean spectra in the absorber rest frames ranging from 1240 to ∼2800 Å, and composite spectra of samples matching the ‘DLA’ QSOs in i-band magnitude and emission redshift zem, but without absorption lines. By comparing the slopes of these composite spectra with their matched counterparts, we find no sign of reddening in the ensemble of the absorbers from these samples. Owing to both the unprecedently large sizes of the DLA samples themselves and the non-DLA SDSS QSO sample, from which we can draw our matching spectra, we can place very tight limits for this non-detection (〈E(B−V)〉=−0.0013 ± 0.0025 (DR5) and 〈E(B−V)〉=−0.0017 ± 0.0022 (DR7). Interestingly, when applying our technique to the samples of York et al., Vanden Berk et al. (intervening and intrinsic Mg ii absorbers) and the smaller DLA subsample and pool of comparison QSOs of Vladilo et al., we do recover their results, i.e. detect the same amount of reddening as these authors do. Furthermore, we have tested whether subsamples of our large sample in categories involving the absorbers (H i column densities, presence or absence of accompanying metal absorption, absorber redshift) or the background quasars (emission redshift, brightness) do reveal dust extinction, but found no trends. These results are at odds with both detections of dust reddening from previous studies and expectations from observations of high-redshift galaxies.
Abstract
Studying the flow of baryons into and out of galaxies is an important part of understanding the evolution of galaxies over time. We present a detailed case study of the environment around an ...intervening Ly α absorption line system at zabs = 0.633, seen towards the quasar J0423−0130 (zQSO = 0.915). We detect with ALMA the 12CO(2–1), 12CO(3–2), and 1.2 mm continuum emission from a galaxy at the redshift of the Ly α absorber at a projected distance of 135 kpc. From the ALMA detections, we infer interstellar medium conditions similar to those in low-redshift luminous infrared galaxies. Director's Discretionary Time (DDT) Multi-Unit Spectroscopic Explorer (MUSE) integral field unit observations reveal the optical counterpart of the 12CO emission line source and three additional emission line galaxies at the absorber redshift, which together form a galaxy group. The 12CO emission line detections originate from the most massive galaxy in this group. While we cannot exclude that we miss a fainter host, we reach a dust-uncorrected star formation rate (SFR) limit of >0.3 M⊙yr−1 within 100 kpc from the sightline to the background quasar. We measure the dust-corrected SFR (ranging from 3 to 50 M⊙ yr−1), the morpho-kinematics and the metallicities of the four group galaxies to understand the relation between the group and the neutral gas probed in absorption. We find that the Ly α absorber traces either an outflow from the most massive galaxy or intragroup gas. This case study illustrates the power of combining ALMA and MUSE to obtain a census of the cool baryons in a bounded structure at intermediate redshift.
In order to understand which process (e.g. galactic winds, cold accretion) is responsible for the cool (T ∼ 104 K) halo gas around galaxies, we embarked on a programme to study the star formation ...properties of galaxies selected by their Mg ii absorption signature in quasar spectra. Specifically, we searched for the Hα line emission from galaxies near very strong z ≃ 2 Mg ii absorbers (with rest-frame equivalent width
Å) because these could be the signposts of outflows or inflows. Surprisingly, we detect Hα from only four hosts out of 20 sightlines (and two out of the 19 H i-selected sightlines), despite reaching a star formation rate (SFR) sensitivity limit of 2.9 M⊙ yr−1 (5σ) for a Chabrier initial mass function. This low success rate (4/20) is in contrast with our z ≃ 1 survey where we detected 66 per cent (14/21) of the Mg ii hosts (down to 0.6 M⊙ yr−1; 5σ). Taking into account the difference in sensitivity between the two surveys, we should have been able to detect ≥11.4 (≥7.6) of the 20 z ≃ 2 hosts - assuming that SFR evolves as ∝(1 + z)γ with γ= 2.5 (or γ= 0) respectively - whereas we found only four galaxies. Interestingly, all the z = 2 detected hosts have observed SFRs ≳ 9 M⊙ yr−1, well above our sensitivity limit, while at z = 1 they all have SFR < 9 M⊙ yr−1, an evolution that is in good agreement with the evolution of the SFR main sequence, i.e. with γ= 2.5. Moreover, we show that the z = 2 undetected hosts are not hidden under the quasar continuum after stacking our data. They also cannot be outside our surveyed area as this latter option runs against our sample selection criteria (
Å) and the known W
λ2796
r-impact parameter relation for low-ionization ions. Hence, strong Mg ii absorbers could trace star-formation-driven winds in low-mass haloes (M
h≤ 1010.6 M⊙), provided that the winds do not extend beyond 20 kpc in order not to violate the evolution of the absorber number density dN/dz (Mg ii). Alternatively, our results imply that z = 2 galaxies traced by strong Mg ii absorbers do not form stars at a rate expected (3-10 M⊙ yr−1) for their (halo or stellar) masses, supporting the existence of a transition in accretion efficiency at M
h≃ 1011 M⊙. This scenario can explain both the detections and the non-detections.
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