New criteria for the selection of galaxy close pairs from cosmological simulations: evolution of the major and minor merger fraction in MUSE deep fields

International audienceIt is still a challenge to assess the merger fraction of galaxies at different cosmic epochs in order to probe the evolution of their mass assembly. Using the Illustris cosmological simulation project, we investigate the relation between the separation of galaxies in a pair, both in velocity and projected spatial separation space, and the probability that these interacting galaxies will merge in the future. From this analysis, we propose a new set of criteria to select close pairs of galaxies along with a new corrective term to be applied to the computation of the galaxy merger fraction. We then probe the evolution of the major and minor merger fraction using the latest MUSE deep observations over the Hubble Ultra Deep Field, Hubble Deep Field South, COSMOS-Gr30 and Abell 2744 regions. From a parent sample of 2483 galaxies with spectroscopic redshifts, we identify 366 close pairs spread over a large range of redshifts (0.2 < z < 6) and stellar masses (10 7 − 10 11 M). Using the stellar mass ratio between the secondary and primary galaxy as a proxy to split the sample into major, minor and very minor mergers, we found a total of 183 major, 142 minor and 47 very minor close pairs corresponding to a mass ratio range of 1:1-1:6, 1:6-1:100 and lower than 1:100, respectively. Due to completeness issues, we do not consider the very minor pairs in the analysis. Overall, the major merger fraction increases up to z ≈ 2 − 3 reaching 25% for pairs with the most massive galaxy with a stellar mass M ≥ 10 9.5 M. Beyond this redshift, the fraction decreases down to ∼ 5% at z ≈ 6. The major merger fraction for lower mass primary galaxies M ≤ 10 9.5 M , seems to follow a more constant evolutionary trend with redshift. Thanks to the addition of new MUSE fields and new selection criteria, the increased statistics of the pair samples allow to narrow significantly the error bars compared to our previous analysis (Ventou et al. 2017). The evolution of the minor merger fraction is roughly constant with cosmic time, with a fraction of 20% at z < 3 and a slow decrease between 3 ≤ z ≤ 6 to 8 − 13%

Scaling relations of z ∼ 0.25–1.5 galaxies in various environments from the morpho-kinematics analysis of the MAGIC sample

Context. The evolution of galaxies is influenced by many physical processes, which may vary depending on their environment. Aims. We combine Hubble Space Telescope (HST) and Multi-Unit Spectroscopic Explorer (MUSE) data of galaxies at 0.25-1.5 to probe the impact of environment on the size-mass relation, the main sequence (MS) relation, and the Tully-Fisher relation (TFR). Methods. We perform a morpho-kinematics modelling of 593 [O-II] emitters in various environments in the COSMOS area from the MUSE-gAlaxy Groups In Cosmos survey. The HST F814W images are modelled with a bulge-disk decomposition to estimate their bulge-disk ratio, effective radius, and disk inclination. We use the [O-II]λλ3727, 3729 doublet to extract the galaxies ionised gas kinematics maps from the MUSE cubes, and we model those maps for a sample of 146 [O-II] emitters, including bulge and disk components constrained from morphology and a dark matter halo. Results. We find an offset of 0.03 dex (1 significant) on the size-mass relation zero point between the field and the large structure sub-samples, with a richness threshold of N=10 to separate between small and large structures, and of 0.06 dex (2) with N=20. Similarly, we find a 0.1 dex (2A) difference on the MS relation with N=10 and 0.15 dex (3) with N=20. These results suggest that galaxies in massive structures are smaller by 14% and have star formation rates reduced by a factor of 1.31.5 with respect to field galaxies at z 0.7. Finally, we do not find any impact of the environment on the TFR, except when using N=20 with an offset of 0.04 dex (1). We discard the effect of quenching for the largest structures, which would lead to an offset in the opposite direction. We find that, at z0.7, if quenching impacts the mass budget of galaxies in structures, these galaxies would have been affected quite recently and for roughly 0.7-+1.5 Gyr. This result holds when including the gas mass but vanishes once we include the asymmetric drift correction

The MUSE Hubble Ultra Deep Field Survey:II. Spectroscopic redshifts and comparisons to color selections of high-redshift galaxies

We have conducted a two-layered spectroscopic survey (1'x1' ultra deep and 3'x3' deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for HST continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z&gt;3 and to HST/F775W magnitudes as faint as ~30 mag (AB, 1-sigma). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field. We assessed redshifts mainly with the spectral features [OII] at z~20% up to 28-29 mag and ~27 mag, respectively. We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures ~80% of the targeted z~2.7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to ~20-40%. We empirically redefine the selection boundaries to make an attempt to improve them to ~60%. The revised boundaries allow bluer colors that capture Lya emitters with high Lya equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog

Scaling relations of z ~ 0.25-1.5 galaxies in various environments from the morpho-kinematics analysis of the MAGIC sample

Galaxie

The MUSE Hubble Ultra Deep Field Survey:II. Spectroscopic redshifts and comparisons to color selections of high-redshift galaxies

We have conducted a two-layered spectroscopic survey (1'x1' ultra deep and 3'x3' deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for HST continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z>3 and to HST/F775W magnitudes as faint as ~30 mag (AB, 1-sigma). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field. We assessed redshifts mainly with the spectral features [OII] at z<1.5 (473 objects) and Lya at 2.9<z<6.7 (692 objects). With respect to F775W magnitude, a 50% completeness is reached at 26.5 mag for ultra deep and 25.5 mag for deep fields, and the completeness remains >~20% up to 28-29 mag and ~27 mag, respectively. We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures ~80% of the targeted z~2.7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to ~20-40%. We empirically redefine the selection boundaries to make an attempt to improve them to ~60%. The revised boundaries allow bluer colors that capture Lya emitters with high Lya equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog.Comment: 26 pages, 26 figures, 4 tables, accepted for publication in A&A (MUSE UDF Series Paper II), the redshift catalogs will be available at the CD

FROM GALAXY PAIRS COUNT TO MASSIVE BLACK HOLE MERGERS: PROSPECTS FOR GRAVITATIONAL WAVES DETECTION

International audienceOur understanding of the seed and evolution of black holes over cosmic time will make a huge step forward in the next decades thanks to gravitational waves. However, predictions of the BH merger rate and detections by new experiments such as LISA are based so far on cosmological simulations only, which do not resolve yet the dwarf galaxies (M < 10 9 M) population. Thanks to the analysis of VLT/MUSE deep fields, we show that such predictions can now be based on measurements of the galaxy merger rate over 12.5 Gyrs of galaxy evolution and covering a broad range of galaxy stellar masses (10 7 − 10 11 M), thus extending into the low-mass dwarf galaxy regime

FROM GALAXY PAIRS COUNT TO MASSIVE BLACK HOLE MERGERS: PROSPECTS FOR GRAVITATIONAL WAVES DETECTION

International audienceOur understanding of the seed and evolution of black holes over cosmic time will make a huge step forward in the next decades thanks to gravitational waves. However, predictions of the BH merger rate and detections by new experiments such as LISA are based so far on cosmological simulations only, which do not resolve yet the dwarf galaxies (M < 10 9 M) population. Thanks to the analysis of VLT/MUSE deep fields, we show that such predictions can now be based on measurements of the galaxy merger rate over 12.5 Gyrs of galaxy evolution and covering a broad range of galaxy stellar masses (10 7 − 10 11 M), thus extending into the low-mass dwarf galaxy regime

Evidence for ram pressure stripping in a cluster of galaxies at z = 0.7

International audienceMUSE observations of the cluster of galaxies CGr32 (M 200 2 × 10 14 M) at z = 0.73 reveal the presence of two massive star forming galaxies with extended tails of diffuse gas detected in the [O ii]λλ3727-3729Å emission-line doublet. The tails, which have a cometary shape with a typical surface brightness of a few 10 −18 erg s −1 cm −2 arcsec −2 , extend up to 100 kpc (projected distance) from the galaxy discs and are not associated to any stellar component. All this observational evidence suggests that the gas has been removed during a ram-pressure stripping event. This observation is thus the first evidence that dynamical interactions with the intracluster medium were active when the Universe had only half of its present age. The density of the gas derived using the observed [O ii]λ3729/[O ii]λ3726 line ratio implies a very short recombination time, suggesting that a source of ionisation is necessary to keep the gas ionised within the tail

Evidence for ram pressure stripping in a cluster of galaxies at z = 0.7

International audienceMUSE observations of the cluster of galaxies CGr32 (M 200 2 × 10 14 M) at z = 0.73 reveal the presence of two massive star forming galaxies with extended tails of diffuse gas detected in the [O ii]λλ3727-3729Å emission-line doublet. The tails, which have a cometary shape with a typical surface brightness of a few 10 −18 erg s −1 cm −2 arcsec −2 , extend up to 100 kpc (projected distance) from the galaxy discs and are not associated to any stellar component. All this observational evidence suggests that the gas has been removed during a ram-pressure stripping event. This observation is thus the first evidence that dynamical interactions with the intracluster medium were active when the Universe had only half of its present age. The density of the gas derived using the observed [O ii]λ3729/[O ii]λ3726 line ratio implies a very short recombination time, suggesting that a source of ionisation is necessary to keep the gas ionised within the tail

Scaling relations of z similar to 0.25-1.5 galaxies in various environments from the morpho-kinematics analysis of the MAGIC sample

Context. The evolution of galaxies is influenced by many physical processes, which may vary depending on their environment.Aims. We combine Hubble Space Telescope (HST) and Multi-Unit Spectroscopic Explorer (MUSE) data of galaxies at 0.25 less than or similar to z less than or similar to 1.5 to probe the impact of environment on the size-mass relation, the main sequence (MS) relation, and the Tully-Fisher relation (TFR).Methods. We perform a morpho-kinematics modelling of 593 [O II] emitters in various environments in the COSMOS area from the MUSE-gAlaxy Groups In Cosmos survey. The HST F814W images are modelled with a bulge-disk decomposition to estimate their bulge-disk ratio, effective radius, and disk inclination. We use the [O II] lambda lambda 3727, 3729 doublet to extract the galaxies' ionised gas kinematics maps from the MUSE cubes, and we model those maps for a sample of 146 [O II] emitters, including bulge and disk components constrained from morphology and a dark matter halo.Results. We find an offset of 0.03 dex (1 sigma - significant) on the size-mass relation zero point between the field and the large structure sub-samples, with a richness threshold of N = 10 to separate between small and large structures, and of 0.06 dex (2 sigma) with N = 20. Similarly, we find a 0.1 dex (2 sigma) difference on the MS relation with N = 10 and 0.15 dex (3 sigma) with N = 20. These results suggest that galaxies in massive structures are smaller by 14% and have star formation rates reduced by a factor of 1.3-1.5 with respect to field galaxies at z approximate to 0.7. Finally, we do not find any impact of the environment on the TFR, except when using N = 20 with an offset of 0.04 dex (1 sigma). We discard the effect of quenching for the largest structures, which would lead to an offset in the opposite direction. We find that, at z approximate to 0.7, if quenching impacts the mass budget of galaxies in structures, these galaxies would have been affected quite recently and for roughly 0.7-1.5 Gyr. This result holds when including the gas mass but vanishes once we include the asymmetric drift correction