arXiv subjects

Johannes Zabl

Publications and source records attributed to Johannes Zabl.

30 records · Page 2Linked to original sources

arXiv2021

MusE GAs FLOw and Wind (MEGAFLOW) V. The dust/metallicity-anisotropy of the Circum-Galactic Medium

We investigate whether the dust content of the circum-galactic medium (CGM) depends on the location of the quasar sightline with respect to the galaxy major-axis using 13 galaxy-MgII absorber pairs (9 - 81 kpc distance) from the MusE GAs FLOw and Wind (MEGAFLOW) survey at 0.4 < z < 1.4. The dust content of the CGM is obtained from [Zn/Fe] using Ultraviolet and Visual Echelle Spectrograph (UVES) data. When a direct measurement of [Zn/Fe] is unavailable, we estimate the dust depletion from a method which consists in solving for the depletion from multiple singly ionized ions (e.g. MnII, CrII, ZnII) since each ion depletes on dust grains at different rates. We find a positive correlation between the azimuthal angle and [Zn/Fe] with a Pearson's r = 0.70 +/- 0.14. The sightlines along the major axis show [Zn/Fe] < 0.5, whereas the [Zn/Fe] is > 0.8 along the minor axis. These results suggest that the CGM along the minor axis is on average more metal enriched (by ~ 1 dex) than the gas located along the major axis of galaxies provided that dust depletion is a proxy for metallicity. This anisotropic distribution is consistent with recent results on outflow and accretion in hydro-dynamical simulations.

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arXiv2020

MusE GAs FLOw and Wind (MEGAFLOW) VII. A NOEMA pilot program to probe molecular gas in galaxies with measured circumgalactic gas flows

We present a pilot program using IRAM's NOrthern Extended Millimeter Array (NOEMA) to probe the molecular gas reservoirs of six $z=0.6-1.1$ star-forming galaxies whose circumgalactic medium has been observed in absorption along quasar lines-of-sight as part of the MusE GAs FLOw and Wind (MEGAFLOW) survey and for which we have estimates of either the accretion or the outflow rate. This program is motivated by testing the quasi equilibrium model and the compaction scenario describing the evolution of galaxies along the main sequence of star formation, which imply tight relations between the gas content, the star formation activity, and the amount of gas flowing in and out. We report individual carbon monoxide CO(4-3), CO(3-2) and dust continuum upper limits, as well as stacked CO detections over the whole sample and the three galaxies identified with outflows. The resulting molecular gas fractions and depletion times are compatible with published scaling relations established within a mass-selected sample, indicating that galaxies selected through their absorption follow similar relations on average. We further detect the dust continuum of three of the quasars and a strong emission line in one of them, which we identify as CO(4-3). Extending the sample to more galaxies and deeper observations will enable to quantify how the molecular gas fraction and depletion time depend on the inflow and ouflow rates.

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arXiv2020

The Fundamental Plane of Massive Quiescent Galaxies at z~2

We examine the Fundamental Plane (FP) and mass-to-light ratio ($M/L$) scaling relations using the largest sample of massive quiescent galaxies at $1.5 11.26$, subset of 8 quiescent galaxies at $z>2$, from Stockmann et al. (2020), we show that they cannot passively evolve to the local Coma cluster relation alone and must undergo significant structural evolution to mimic the sizes of local massive galaxies. The evolution of the FP and $M/L$ scaling relations, from $z=2$ to present-day, for this subset are consistent with passive aging of the stellar population and minor merger structural evolution into the most massive galaxies in the Coma cluster and other massive elliptical galaxies from the MASSIVE Survey. Modeling the luminosity evolution from minor merger added stellar populations favors a history of merging with "dry" quiescent galaxies.

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arXiv2020

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

Lyman$-α$ (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 $z\approx3.3$ Ly$α$ emitters (LAEs) with a median Ly$α$ flux (luminosity) of $\approx 10^{-17}~\rm erg~cm^{-2}~s^{-1}$ ($\approx10^{42}~\rm erg~s^{-1}$) and a median star formation rate (SFR) of $\approx1.3 \rm M_{\odot} yr^{-1}$ (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 8 background quasars, must be centered on the systemic redshift, we measure an average velocity offset, V$_{\rm offset} = 171 \pm 8$ $\rm km s^{-1}$, between the Ly$α$ emission peak and the systemic redshift. The observed V$_{\rm offset}$ is lower by factors of $\approx1.4$ and $\approx2.6$ 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 V$_{\rm offset}$ is correlated with the full width at half-maximum of the red peak of the Ly$α$ line, and anti-correlated with the rest-frame equivalent width. Moreover, we find that $V_{\rm offset}$ is correlated with SFR with a sub-linear scaling relation, V$_{\rm offset}\propto \rm SFR^{0.16\pm0.03}$. Adopting the mass scaling for main sequence galaxies, such a relation suggests that V$_{\rm offset}$ scales with the circular velocity of the dark matter halos hosting the LAEs.

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arXiv2020

Stellar Velocity Dispersion of a Massive Quenching Galaxy at z=4.01

We present the first stellar velocity dispersion measurement of a massive quenching galaxy at z=4.01. The galaxy is first identified as a massive z>~4 galaxy with suppressed star formation from photometric redshifts based on deep multi-band data in the UKIDSS Ultra Deep Survey field. A follow-up spectroscopic observation with MOSFIRE on Keck revealed strong multiple absorption features, which are identified as Balmer absorption lines, giving a secure redshift of z=4.01. Thanks to the high S/N of the spectrum, we are able to estimate the stellar velocity dispersion, sigma=268+/-59 km/s. This velocity dispersion is consistent with that of massive galaxies today, implying no significant evolution in stellar velocity dispersion over the last 12 Gyr. Based on an upper limit on its physical size from deep optical images (r_eff<1.3 kpc), we find that its dynamical mass is consistent with the stellar mass inferred from photometry. Furthermore, the galaxy is located on the mass fundamental plane extrapolated from lower redshift galaxies. Combining all these results, we find that the velocity dispersion does not significantly evolve with redshift, although the size and mass of massive quenched galaxies do. This suggests that the mass in the core of massive galaxies does not evolve significantly, while most of the mass growth occurs in the outskirts of the galaxies, which also increases the size. This picture is consistent with a two-phase formation scenario in which mass and size growth is due to accretion in the outskirts of galaxies via mergers.

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arXiv2019

Quiescent galaxies 1.5 billion years after the Big Bang and their progenitors

We report two secure ($z=3.775, 4.012$) and one tentative ($z\approx3.767$) spectroscopic confirmations of massive and quiescent galaxies through $K$-band observations with Keck/MOSFIRE and VLT/X-Shooter. The stellar continuum emission, the absence of strong nebular emission lines and the lack of significant far-infrared detections confirm the passive nature of these objects, disfavoring the alternative solution of low-redshift dusty star-forming interlopers. We derive stellar masses of $\mathrm{log}(M_{\star}/M_\odot)\sim11$ and ongoing star formation rates placing these galaxies $\gtrsim 1-2$ dex below the main sequence at their redshifts. The adopted parametrization of the star formation history suggests that these sources experienced a strong ($\langle \rm SFR \rangle \sim 1200-3500\,M_\odot\,\mathrm{yr}^{-1}$) and short ($\sim 50$ Myr) burst of star formation, peaking $\sim 150-500$ Myr before the time of observation, all properties reminiscent of the characteristics of sub-millimeter galaxies (SMGs) at $z>4$. We investigate this connection by comparing the comoving number densities and the properties of these two populations. We find a fair agreement only with the deepest sub-mm surveys detecting not only the most extreme starbursts, but also more normal galaxies. We support these findings by further exploring the Illustris-TNG cosmological simulation, retrieving populations of both fully quenched massive galaxies at $z\sim3-4$ and SMGs at $z\sim4-5$, with number densities and properties in agreement with the observations at $z\sim3$, but in increasing tension at higher redshift. Nevertheless, as suggested by the observations, not all the progenitors of quiescent galaxies at these redshifts shine as bright SMGs in their past and, similarly, not all bright SMGs quench by $z\sim3$, both fractions depending on the threshold assumed to define the SMGs themselves.

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arXiv2019

X-shooter Spectroscopy and HST Imaging of 15 Ultra Massive Quiescent Galaxies at $z\gtrsim2$

We present a detailed analysis of a large sample of spectroscopically confirmed ultra-massive quiescent galaxies (${\rm{log}}(M_{\ast}/M_{\odot})\sim11.5$) at $z\gtrsim2$. This sample comprises 15 galaxies selected in the COSMOS and UDS fields by their bright K-band magnitudes and followed up with VLT/X-shooter spectroscopy and HST/WFC3 $H_{F160W}$ imaging. These observations allow us to unambiguously confirm their redshifts ascertain their quiescent nature and stellar ages, and to reliably assess their internal kinematics and effective radii. We find that these galaxies are compact, consistent with the high mass end of the mass-size relation for quiescent galaxies at $z=2$. Moreover, the distribution of the measured stellar velocity dispersions of the sample is consistent with the most massive local early-type galaxies from the MASSIVE Survey showing that evolution in these galaxies, is dominated by changes in size. The HST images reveal, as surprisingly high, that $40\ \%$ of the sample have tidal features suggestive of mergers and companions in close proximity, including three galaxies experiencing ongoing major mergers. The absence of velocity dispersion evolution from $z=2$ to $0$, coupled with a doubling of the stellar mass, with a factor of four size increase and the observed disturbed stellar morphologies support dry minor mergers as the primary drivers of the evolution of the massive quiescent galaxies over the last 10 billion years.

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arXiv2019

MusE GAs FLOw and Wind (MEGAFLOW) IV: A two sightline tomography of a galactic wind

Galactic outflows are thought to eject baryons back out to the circum-galactic medium (CGM). Studies based on metal absorption lines (MgII in particular) in the spectra of background quasars indicate that the gas is ejected anisotropically, with galactic winds likely leaving the host in a bi-conical flow perpendicular to the galaxy disk. In this paper, we present a detailed analysis of an outflow from a z = 0.7 "green-valley" galaxy (log($M_*$/$\mathrm{M}_\odot$) = 9.9; SFR = 0.5 $\mathrm{M}_\odot\,\mathrm{yr}^{-1}$) probed by two background sources part of the MUSE Gas Flow and Wind (MEGAFLOW) survey. Thanks to a fortuitous configuration with a background quasar (SDSSJ1358+1145) and a bright background galaxy at $z = 1.4$, both at impact parameters of $\approx 15\,\mathrm{kpc}$, we can - for the first time - probe both the receding and approaching components of a putative galactic outflow around a distant galaxy. We measure a significant velocity shift between the MgII absorption from the two sightlines ($84\pm17\,\mathrm{km}\,\mathrm{s}^{-1}$), which is consistent with the expectation from our simple fiducial wind model, possibly combined with an extended disk contribution.

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arXiv2019

MusE GAs FLOw and Wind (MEGAFLOW) III: galactic wind properties using background quasars

We present results from our on-going MusE GAs FLOw and Wind (MEGAFLOW) survey, which consists of 22 quasar lines-of-sight, each observed with the integral field unit (IFU) MUSE and the UVES spectrograph at the ESO Very Large Telescopes (VLT). The goals of this survey are to study the properties of the circum-galactic medium around $z\sim1$ star-forming galaxies. The absorption-line selected survey consists of 79 strong \MgII\ absorbers (with rest-frame equivalent width (REW)$\gtrsim$0.3Å) and, currently, 86 associated galaxies within 100 projected~kpc of the quasar with stellar masses ($M_\star$) from $10^9$ to $10^{11}$ \msun. We find that the cool halo gas traced by \MgII\ is not isotropically distributed around these galaxies, as we show the strong bi-modal distribution in the azimuthal angle of the apparent location of the quasar with respect to the galaxy major-axis. This supports a scenario in which outflows are bi-conical in nature and co-exist with a coplanar gaseous structure extending at least up to 60 to 80 kpc. Assuming that absorbers near the minor axis probe outflows, the current MEGAFLOW sample allowed us to select 26 galaxy-quasar pairs suitable for studying winds. From this sample, using a simple geometrical model, we find that the outflow velocity only exceeds the escape velocity when $M_{\star}\lesssim 4\times10^9$~\msun, implying the cool material is likely to fall back except in the smallest halos. Finally, we find that the mass loading factor $η$, the ratio between the ejected mass rate and the star formation rate (SFR), appears to be roughly constant with respect to the galaxy mass.

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arXiv2019

MusE GAs FLOw and Wind (MEGAFLOW) II. A study of gas accretion around $z\approx1$ star-forming galaxies with background quasars

We use the MusE GAs FLOw and Wind (MEGAFLOW) survey to study the kinematics of extended disk-like structures of cold gas around $z\approx1$ star-forming galaxies. The combination of VLT/MUSE and VLT/UVES observations allows us to connect the kinematics of the gas measured through MgII quasar absorption spectroscopy to the kinematics and orientation of the associated galaxies constrained through integral field spectroscopy. Confirming previous results, we find that the galaxy-absorber pairs of the MEGAFLOW survey follow a strong bimodal distribution, consistent with a picture of MgII absorption being predominantly present in outflow cones and extended disk-like structures. This allows us to select a bona-fide sample of galaxy-absorber pairs probing these disks for impact parameters of 10-70 kpc. We test the hypothesis that the disk-like gas is co-rotating with the galaxy disks, and find that for 7 out of 9 pairs the absorption velocity shares the sign of the disk velocity, disfavouring random orbits. We further show that the data are roughly consistent with inflow velocities and angular momenta predicted by simulations, and that the corresponding mass accretion rates are sufficient to balance the star formation rates.

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arXiv2018

The MUSE Hubble Ultra Deep Field Survey XI. Constraining the low-mass end of the stellar mass - star formation rate relation at $z<1$

Star-forming galaxies have been found to follow a relatively tight relation between stellar mass ($M_{*}$) and star formation rate (SFR), dubbed the `star formation sequence'. A turnover in the sequence has been observed, where galaxies with $M_{*} < 10^{10} {\rm M}_{\odot}$ follow a steeper relation than their higher mass counterparts, suggesting that the low-mass slope is (nearly) linear. In this paper, we characterise the properties of the low-mass end of the star formation sequence between $7 \leq \log M_{*}[{\rm M}_{\odot}] \leq 10.5$ at redshift $0.11 < z < 0.91$. We use the deepest MUSE observations of the Hubble Ultra Deep Field and the Hubble Deep Field South to construct a sample of 179 star-forming galaxies with high signal-to-noise emission lines. Dust-corrected SFRs are determined from H$β$ $λ4861$ and H$α$ $λ6563$. We model the star formation sequence with a Gaussian distribution around a hyperplane between $\log M_{*}$, $\log {\rm SFR}$, and $\log (1+z)$, to simultaneously constrain the slope, redshift evolution, and intrinsic scatter. We find a sub-linear slope for the low-mass regime where $\log {\rm SFR}[{\rm M}_{\odot}/{\rm yr}] = 0.83^{+0.07}_{-0.06} \log M_{*}[{\rm M}_{\odot}] + 1.74^{+0.66}_{-0.68} \log (1+z)$, increasing with redshift. We recover an intrinsic scatter in the relation of $σ_{\rm intr} = 0.44^{+0.05}_{-0.04}$ dex, larger than typically found at higher masses. As both hydrodynamical simulations and (semi-)analytical models typically favour a steeper slope in the low-mass regime, our results provide new constraints on the feedback processes which operate preferentially in low-mass halos.

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arXiv2017

A massive, dead disk galaxy in the early Universe

At redshift z = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation(1-4). It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions(5,6), but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies(7). Here we report an analysis of the stellar populations and kinematics of a lensed z = 2.1478 compact galaxy, which surprisingly turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst(8). The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo(9). This result confirms previous indirect indications(10-13) that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.

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