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Register a new userMusE GAs FLOw and Wind (MEGAFLOW) IV: A two sightline tomography of a galactic wind
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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 ($84pm17,mathrm{km},mathrm{s}^{-1}$), which is consistent with the expectation from our simple fiducial wind model, possibly combined with an extended disk contribution.
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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 $zsim1$ star-forming galaxies. The absorption-line selected survey consists of 79 strong MgII absorbers (with rest-frame equivalent width (REW)$gtrsim$0.3AA) and, currently, 86 associated galaxies within 100 projected~kpc of the quasar with stellar masses ($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 $M_{star}lesssim 4times10^9$~msun, implying the cool material is likely to fall back except in the smallest halos. Finally, we find that the mass loading factor $eta$, the ratio between the ejected mass rate and the star formation rate (SFR), appears to be roughly constant with respect to the galaxy mass.
Using deep (11.2hr) VLT/MUSE data from the MEGAFLOW survey, we report the first detection of extended MgII emission from a galaxys halo that is probed by a quasar sightline. The MgII $lambdalambda$ 2796,2803 emission around the $z = 0.702$ galaxy ($log(M_*/mathrm{M_odot}) = 10.05^{+0.15}_{-0.11}$) is detected out to $approx$25 kpc from the central galaxy and covers $1.0times10^3$ kpc$^2$ above a surface brightness of $14times10^{-19} mathrm{erg} mathrm{s}^{-1} mathrm{cm}^{-2},mathrm{arcsec}^{-2}$ ($2 sigma$; integrated over 1200 km s$^{-1}$ =19A and averaged over $1.5 ;mathrm{arcsec}^2$). The MgII emission around this highly inclined galaxy ($simeq$75 deg) is strongest along the galaxys projected minor axis, consistent with the MgII gas having been ejected from the galaxy into a bi-conical structure. The quasar sightline, which is aligned with the galaxys minor axis, shows strong MgII $lambda$2796 absorption (EW$_0$ = 1.8A) at an impact parameter of 39kpc from the galaxy. Comparing the kinematics of both the emission and the absorption - probed with VLT/UVES -, to the expectation from a simple toy model of a bi-conical outflow, we find good consistency when assuming a relatively slow outflow ($v_mathrm{out}= 130;mathrm{km},mathrm{s}^{-1}$). We investigate potential origins of the extended MgII emission using simple toy models. With continuum scattering models we encounter serious difficulties in explaining the luminosity of the MgII halo and in reconciling density estimates from emission and absorption. Instead, we find that shocks might be a more viable source to power the extended MgII (and non-resonant [OII]) emission.
The physical properties of galactic winds are one of the keys to understand galaxy formation and evolution. These properties can be constrained thanks to background quasar lines of sight (LOS) passing near star-forming galaxies (SFGs). We present the first results of the MusE GAs FLOw and Wind (MEGAFLOW) survey obtained of 2 quasar fields which have 8 MgII absorbers of which 3 have rest-equivalent width greater than 0.8 AA. With the new Multi Unit Spectroscopic Explorer (MUSE) spectrograph on the Very Large Telescope (VLT), we detect 6 (75$%$) MgII host galaxy candidates withing a radius of 30 arcsec from the quasar LOS. Out of these 6 galaxy--quasar pairs, from geometrical arguments, one is likely probing galactic outflows, two are classified as ambiguous, two are likely probing extended gaseous disks and one pair seems to be a merger. We focus on the wind$-$pair and constrain the outflow using a high resolution quasar spectra from Ultraviolet and Visual Echelle Spectrograph (UVES). Assuming the metal absorption to be due to gas flowing out of the detected galaxy through a cone along the minor axis, we find outflow velocities of the order of $approx$ 150 km/s (i.e. smaller than the escape velocity) with a loading factor, $eta =dot M_{rm out}/$SFR, of $approx$ 0.7. We see evidence for an open conical flow, with a low-density inner core. In the future, MUSE will provide us with about 80 multiple galaxy$-$quasar pairs in two dozen fields.
We use the MusE GAs FLOw and Wind (MEGAFLOW) survey to study the kinematics of extended disk-like structures of cold gas around $zapprox1$ 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.
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 Pearsons 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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