Frontiers of Galaxy Evolution : Time-Domain Observations and 3D Spectroscopy

Understanding the formation and evolution of galaxies through cosmic time has been a central focus of astrophysics in the last decades: how did the interplay between dark matter structure formation, star formation, galaxy merging, and active galactic nuclei (AGN) give rise to the observed galaxy properties at different redshifts? This thesis presents innovative observational approaches to two aspects of this problem: finding and studying AGN through their variability, and making a first systematic census of galaxy mergers at z > 1 through three-dimensional spectroscopy. First we present a new and simple technique for selecting extensive, complete, and pure quasar samples via their intrinsic variability, parameterizing the single-band light-curve structure function through a power-law to identify quasars among other variable and non-variable sources. Using extensive multi-epoch observations from SDSS Stripe 82 containing ~60 epochs taken over 8 years, we demonstrate the power of this approach. The presented algorithm identifies quasars with a completeness and purity above 90% at all redshifts. Even for Pan-STARRS 1 mock data of only 6 epochs over 3 years, variability is still an encouragingly efficient quasar classifier. Data on intrinsic quasar variability enable a wide range of astrophysical science. We quantify the color variability, confirming and greatly fleshing out previous claims, that quasars become bluer as they brighten. We find a strong redshift dependence of this blueing, which we can attribute to emission lines contributing to the SDSS bands at di fferent redshifts. We find that the color variations of single quasars are much more pronounced than the ranges in color seen in time-averaged ensembles of quasars. This indicates, that the observed color variations cannot be explained by changes in the mean steady state AGN accretion rate, but must arise from accretion disk ‘hotspots’ or similar phenomena. In the second, distinct part of the thesis, we present the first large sample of morphologically selected galaxy mergers with three-dimensional spectroscopy at z~1.5. With individual masses and star formation rates derived from multi-band photometry, we created emission line maps from the slitless grism spectroscopy of 3D-HST as proxy for star formation maps, providing a comprehensive empirical picture of where star formation takes place in galaxy mergers at the epoch, where the cosmic star formation and merger rates peaked. We find that a broad range of star formation morphologies occur at all redshifts, irrespective of star formation rate and total stellar mass, in these mergers. An initial illustrative comparison to a set of cosmological simulations shows, that simulated mergers with similar mass and gas content show star formation in both merger components far more often than for the observed 3D-HST mergers. This suggests that mergers at z~1.5 most commonly happen between galaxies of distinctly di erent gas fractions

Climbing to the top of the galactic mass ladder: evidence for frequent prolate-like rotation among the most massive galaxies

We present the stellar velocity maps of 25 massive early type galaxies located in dense environments observed with MUSE. Galaxies are selected to be brighter than M_K=-25.7 magnitude, reside in the core of the Shapley Super Cluster or be the brightest galaxy in clusters richer than the Virgo Cluster. We thus targeted galaxies more massive than 10^12 Msun and larger than 10 kpc (half-light radius). The velocity maps show a large variety of kinematic features: oblate-like regular rotation, kinematically distinct cores and various types of non-regular rotation. The kinematic misalignment angles show that massive galaxies can be divided into two categories: those with small or negligible misalignment, and those with misalignment consistent with being 90 degrees. Galaxies in this latter group, comprising just under half of our galaxies, have prolate-like rotation (rotation around the major axis). Among the brightest cluster galaxies the incidence of prolate-like rotation is 50 per cent, while for a magnitude limited sub-sample of objects within the Shapley Super Cluster (mostly satellites), 35 per cent of galaxies show prolate-like rotation. Placing our galaxies on the mass - size diagram, we show that they all fall on a branch extending almost an order of magnitude in mass and a factor of 5 in size from the massive end early-type galaxies, previously recognised as associated with major dissipation-less mergers. The presence of galaxies with complex kinematics and, particularly, prolate-like rotators suggests, according to current numerical simulations, that the most massive galaxies grow predominantly through dissipation-less equal-mass mergers.Comment: 11 pages, 4 figures, accepted to MNRA

The MUSE-Wide survey: A measurement of the Lyα\alpha emitting fraction among z>3z>3 galaxies

We present a measurement of the fraction of Lyman $\alpha$ (Ly$\alpha$) emitters ($X_{\rm{Ly} \alpha}$) amongst HST continuum-selected galaxies at $3<z<6$ with the Multi-Unit Spectroscopic Explorer (MUSE) on the VLT. Making use of the first 24 MUSE-Wide pointings in GOODS-South, each having an integration time of 1 hour, we detect 100 Ly$\alpha$ emitters and find $X_{\rm{Ly} \alpha}\gtrsim0.5$ for most of the redshift range covered, with 29 per cent of the Ly$\alpha$ sample exhibiting rest equivalent widths (rest-EWs) $\leq$ 15\AA. Adopting a range of rest-EW cuts (0 - 75\AA), we find no evidence of a dependence of $X_{\rm{Ly} \alpha}$ on either redshift or UV luminosity.Comment: 10 pages, 5 figures (MNRAS, updated as per version in press

The MUSE-Wide Survey: A determination of the Lyman

We investigate the Lyman α emitter (LAE) luminosity function (LF) within the redshift range 2.9 ≤ z ≤ 6 from the first instalment of the blind integral field spectroscopic MUSE-Wide survey. This initial part of the survey probes a region of 22.2 arcmin2 in the CANDELS/GOODS-S field (24 MUSE pointings with 1h integrations). The dataset provided us with 237 LAEs from which we construct the LAE LF in the luminosity range 42.2 ≤ log LLyα[erg s−1] ≤ 43.5 within a volume of 2.3 × 105 Mpc3. For the LF construction we utilise three different non-parametric estimators: the classical 1/Vmax method, the C− method, and an improved binned estimator for the differential LF. All three methods deliver consistent results, with the cumulative LAE LF being Φ(log L Lyα[erg s−1] = 43.5) ≃ 3 × 10−6 Mpc−3 and Φ(log L Lyα[erg s−1] = 42.2) ≃ 2 × 10−3 Mpc−3 towards the bright and faint end of our survey, respectively. By employing a non-parametric statistical test, and by comparing the full sample to subsamples in redshift bins, we find no supporting evidence for an evolving LAE LF over the probed redshift and luminosity range. Using a parametric maximum-likelihood technique we determine the best-fitting Schechter function parameters $\alpha = -1.84^{+0.42}_{-0.41}$ and $\log L^* [\mathrm{erg\,s}^{-1}] = 42.2^{+0.22}_{-0.16}$ with the corresponding normalisation logϕ*[Mpc−3]= − 2.71. However, the dynamic range in Lyα luminosities probed by MUSE-Wide leads to a strong degeneracy between α and L*. Moreover, we find that a power-law parameterisation of the LF appears to be less consistent with the data compared to the Schechter function, even so when not excluding the X-Ray identified AGN from the sample. When correcting for completeness in the LAE LF determinations, we take into account that LAEs exhibit diffuse extended low surface brightness halos. We compare the resulting LF to one obtained by applying a correction assuming compact point-like emission. We find that the standard correction underestimates the LAE LF at the faint end of our survey by a factor of 2.5. Contrasting our results to the literature we find that at 42.2 ≤ log LLyα[erg s−1] ≲ 42.5 previous LAE LF determinations from narrow-band surveys appear to be affected by a similar bias

The MUSE Hubble Ultra Deep Field Survey - XIV. Evolution of the Lyα\alpha emitter fraction from z = 3 to z = 6

International audienceContext. The Lyα emitter (LAE) fraction, XLAE, is a potentially powerful probe of the evolution of the intergalactic neutral hydrogen gas fraction. However, uncertainties in the measurement of XLAE are still under debate.Aims. Thanks to deep data obtained with the integral field spectrograph Multi Unit Spectroscopic Explorer (MUSE), we can measure the evolution of the LAE fraction homogeneously over a wide redshift range of z ≈ 3–6 for UV-faint galaxies (down to UV magnitudes of M1500 ≈ −17.75). This is a significantly fainter range than in former studies (M1500 ≤ −18.75) and it allows us to probe the bulk of the population of high-redshift star-forming galaxies.Methods. We constructed a UV-complete photometric-redshift sample following UV luminosity functions and measured the Lyα emission with MUSE using the latest (second) data release from the MUSE Hubble Ultra Deep Field Survey.Results. We derived the redshift evolution of XLAE for M1500 ∈ [ − 21.75; −17.75] for the first time with a equivalent width range EW(Lyα) ≥ 65 Å and found low values of XLAE ≲ 30% at z ≲ 6. The best-fit linear relation is XLAE = 0.07+0.06−0.03z − 0.22+0.12−0.24. For M1500 ∈ [ − 20.25; −18.75] and EW(Lyα) ≥ 25 Å, our XLAE values are consistent with those in the literature within 1σ at z ≲ 5, but our median values are systematically lower than reported values over the whole redshift range. In addition, we do not find a significant dependence of XLAE on M1500 for EW(Lyα) ≥ 50 Å at z ≈ 3–4, in contrast with previous work. The differences in XLAE mainly arise from selection biases for Lyman Break Galaxies (LBGs) in the literature: UV-faint LBGs are more easily selected if they have strong Lyα emission, hence XLAE is biased towards higher values when those samples are used.Conclusions. Our results suggest either a lower increase of XLAE towards z ≈ 6 than previously suggested, or even a turnover of XLAE at z ≈ 5.5, which may be the signature of a late or patchy reionization process. We compared our results with predictions from a cosmological galaxy evolution model. We find that a model with a bursty star formation (SF) can reproduce our observed LAE fractions much better than models where SF is a smooth function of time.Key words: dark ages / reionization / first stars / early Universe / cosmology: observations / galaxies: evolution / galaxies: high-redshift / intergalactic mediu

Emission line galaxies beyond the limits of the Hubble UDF: Physical conditions in ultra-faint star forming galaxies

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Emission line galaxies beyond the limits of the Hubble UDF: Physical conditions in ultra-faint star forming galaxies

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Emission line galaxies beyond the limits of the Hubble UDF: Physical conditions in ultra-faint star forming galaxies

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