MUSEQuBES: calibrating the redshifts of Ly α emitters using stacked circumgalactic medium absorption profiles

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>Ly α emission lines are typically found to be redshifted with respect to the systemic redshifts of galaxies, likely due to resonant scattering of Ly α photons. Here, we measure the average velocity offset for a sample of 96 z ≈ 3.3 Ly α emitters (LAEs) with a median Ly α flux (luminosity) of ${\approx}10^{-17}~\rm erg~cm^{-2}~s^{-1}$ (${\approx}10^{42}~\rm erg~s^{-1}$) and a median star formation rate (SFR) of ≈1.3 $\rm M_{\odot }~yr^{-1}$ (not corrected for possible dust extinction), detected by the Multi-Unit Spectroscopic Explorer as part of our MUSEQuBES circumgalactic medium (CGM) survey. By postulating that the stacked CGM absorption profiles of these LAEs, probed by eight background quasars, must be centred on the systemic redshift, we measure an average velocity offset, Voffset = 171\pm 8 km s−1, between the Ly α emission peak and the systemic redshift. The observed Voffset is lower by factors of ≈1.4 and ≈2.6 compared to the velocity offsets measured for narrow-band-selected LAEs and Lyman break galaxies, respectively, which probe galaxies with higher masses and SFRs. Consistent with earlier studies based on direct measurements for individual objects, we find that the Voffset is correlated with the full width at half-maximum of the red peak of the Ly α line, and anticorrelated with the rest-frame equivalent width. Moreover, we find that Voffset is correlated with SFR with a sub-linear scaling relation, $V_{\rm offset}\propto \rm SFR^{0.16\pm 0.03}$. Adopting the mass scaling for main-sequence galaxies, such a relation suggests that Voffset scales with the circular velocity of the dark matter haloes hosting the LAEs.</jats:p>

Predictions for the angular dependence of gas mass flow rate and metallicity in the circumgalactic medium

“…and M = 10 10.5 ± 0.2 M . The redshift of z = 0.5 is chosen to match those of ongoing MUSE surveys of quasar absorbers (Schroetter et al 2019;Hamanowicz et al 2020;Muzahid et al 2020), while the stellar mass corresponds to the mean stellar mass of high column density quasar absorbers (Augustin et al 2018).…”

“…The increasing availability of wide, high throughput and 3D integral-field unit spectrographs allows for studies of absorption fields which will enable statistically robust comparisons with these theoretical expectations. These include programmes on VLT/MUSE (and Keck/KCWI), including MEGAFLOW, MUSEQuBES, MUSE-ALMA Halos, MAGG, and similar surveys (Zabl et al 2019;Muzahid et al 2020;Hamanowicz et al 2020;Lofthouse et al 2020). Our results reveal that a large sample of galaxy-absorber pairs with robust metallicity measurements (including mostly neutral gas traced by higher N (H i) and reliable dust-depletion correction) with impact parameters up to b = 200 kpc at z < 1 are best to uncover the trend of metallicity with azimuthal angle.…”

“…Early efforts started with the AO-equipped near-infrared spectrograph VLT/SINFONI (Bouché et al 2007b;Péroux et al 2011;Péroux et al 2013Péroux et al , 2016Schroetter et al 2015). The potential of this technique for studying the CGM with the wide-field optical spectrograph VLT/MUSE has been further demonstrated (Bouché et al 2016;Schroetter et al 2016;Schroetter et al 2019;Zabl et al 2019;Muzahid et al 2020;Lofthouse et al 2020) as well as with the high spectral resolution optical spectrograph Keck/KCWI (Martin et al 2019a;Nielsen et al 2020). At z abs <1, the MUSE-ALMA Halos survey has measured the kinematics of the neutral, molecular, and ionized gas of the multiphase CGM (Péroux et al 2017;Klitsch et al 2018;Rahmani et al 2018a, b;Péroux et al 2019;Hamanowicz et al 2020).…”

MUSE Analysis of Gas around Galaxies (MAGG) – II: metal-enriched halo gas around z ∼ 1 galaxies

“…Wide-field optical integral field unit (IFU) spectrographs like the Multi Unit Spectroscopic Explorer (MUSE; Bacon et al 2010) at the Very Large Telescope (VLT) have revolutionized the study of CGM by enabling efficient and sensitive spectroscopic surveys complete down to a given flux limit around quasar sightlines (e.g. Fumagalli et al 2016Fumagalli et al , 2017Schroetter et al 2016;Mackenzie et al 2019;Zabl et al 2019;Fossati et al 2019b;Lofthouse et al 2020;Muzahid et al 2020). Such type of surveys allows a more complete characterization of the smallscale galaxy environment, a complete (flux limited) analysis of the CGM-galaxy connection up to 250 kpc from the quasar sightlines, and enables studies of CGM to lower mass galaxies (M * <10 10 M ) at z ≥ 1.…”

“…This survey comprises MUSE observations of 28 fields centred on z = 3.2-4.5 quasars that show strong H I absorption lines at z > 3 in their high-resolution optical spectra, which are therefore ideal to address the Mg II-galaxy connection in an unbiased way at lower redshift. The MUSE data are primarily from our VLT large programme (ID 197.A−0384, PI: M. Fumagalli), which are supplemented by data from the MUSE GTO (PI: J. Schaye; Muzahid et al 2020). The survey strategy and methodology, including sample selection and data processing, have been presented in Lofthouse et al (2020).…”