Galactic-Scale Outflows in Galaxies of the Local Universe

Galactic-scale gas outflows form a crucial ingredient in today’s galaxy evolution mod- els and are thought to regulate the gas contents - and therefore evolution - of galaxies. However, outflows are poorly understood, and thus far have been studied primarily in extreme objects rather than the normal star-forming populations. As such, several out- standing questions remain and determining the prevalence and properties of outflows in normal, star-forming galaxies, as well as their quenching potential is a prerequisite towards obtaining a complete picture of galaxy evolution. Specifically, major questions include: What is the prevalence of outflows in normal galaxies and what are their main drivers and properties? Are the properties of outflows enhanced by the presence of an AGN? What are the kpc-scale properties of outflows? Are outflows seen in all gas phases and what are their relative fractions? This Thesis aims to answers these questions by making use of the largest integrated and IFU spectroscopic data sets currently available such as the SDSS, MaNGA, xCOLD GASS, xGASS and ALFALFA surveys. Using the NaD ISM doublet and a variety of stacking techniques, we investigate the large-scale prevalence and properties of outflows in normal galaxies at z ∼0 with SDSS spectra, the kpc-scale outflow properties and their relation to galaxy properties with MaNGA IFU spectra, and finally investigate the multi- phase (i.e., molecular, neutral and ionised) nature of outflows with a stacking analysis of CO(1-0), H i 21cm, NaD and Hα tracers using the xCOLD GASS, xGASS, ALFALFA and MaNGA surveys. The Thesis finishes off with the investigation of the possible presence of a molecular gas outflow in a high redshift, lensed galaxy for which multitransitional CO and C i spectra were obtained with the IRAM 30m telescope

Dust in the reionization era: ALMA observations of a zz=8.38 Galaxy

We report on the detailed analysis of a gravitationally-lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744. Band 7 observations with the Atacama Large Millimeter Array (ALMA) indicate the proximate detection of a significant 1mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of $z\simeq8$. Deep X-SHOOTER spectra confirms the high redshift identity of A2744_YD4 via the detection of Lyman $\alpha$ emission at a redshift $z$=8.38. The association with the ALMA detection is confirmed by the presence of [OIII] 88$\mu$m emission at the same redshift. Although both emission features are only significant at the 4 $\sigma$ level, we argue their joint detection and the positional coincidence with a high redshift dropout in the HST images confirms the physical association. Analysis of the available photometric data and the modest gravitational magnification ($\mu\simeq2$) indicates A2744_YD4 has a stellar mass of $\sim$ 2$\times$10$^9$ M$_{\odot}$, a star formation rate of $\sim20$ M$_{\odot}$/yr and a dust mass of $\sim$6$\times$10$^{6}$ M$_{\odot}$. We discuss the implications of the formation of such a dust mass only $\simeq$200 Myr after the onset of cosmic reionisation.Comment: Accepted for publication in ApJ

Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization

We report the discovery of Lyman-alpha emission (Ly$\alpha$) in the bright galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at the Keck Observatory. First reported by Roberts-Borsani et al. (2015), it was selected for spectroscopic observations because of its photometric redshift ($z_{phot}=8.57^{+0.22}_{-0.43}$), apparent brightness (H$_{160}=25.26\pm0.09$) and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong oxygen emission in the [4.5] band. With a total integration of $\sim$4.3 hours, our data reveal an emission line at $\simeq$11776 {\AA} which we argue is likely Ly$\alpha$ at a redshift $z_{spec}=8.683^{+0.001}_{-0.004}$, in good agreement with the photometric estimate. The line was detected independently on two nights using different slit orientations and its detection significance is $\sim7.5\sigma$. An overlapping skyline contributes significantly to the uncertainty on the total line flux although the significance of the detected line is robust to a variety of skyline-masking procedures. By direct addition and a Gaussian fit, we estimate a 95\% confidence range of 1.0--2.5$\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$, corresponding to a rest-frame equivalent width of 17--42 {\AA}. EGSY8p7 is the most distant galaxy confirmed spectroscopically to date, and the third luminous source in the EGS field beyond $z_{phot}\gtrsim7.5$ with detectable Ly$\alpha$ emission viewed at a time when the intergalactic medium is believed to be fairly neutral. Although the reionization process was probably patchy, we discuss whether luminous sources with prominent IRAC color excesses may harbor harder ionizing spectra than the dominant fainter population thereby creating earlier ionized bubbles. Further spectroscopic follow-up of such bright sources promises important insight into the early formation of galaxies.Comment: V3: ApJL accepted; 7 pages, 4 figures, 1 tabl

The Mass-Metallicity Relation at z=8: Direct-Method Metallicity Constraints and Near-Future Prospects

Physical properties of galaxies at z>7 are of interest for understanding both the early phases of star formation and the process of cosmic reionization. Chemical abundance measurements offer valuable information on the integrated star formation history, and hence ionizing photon production, as well as the rapid gas accretion expected at such high redshifts. We use reported measurements of [O III] 88$\mu$m emission and star formation rate to estimate gas-phase oxygen abundances in five galaxies at z=7.1-9.1 using the direct T_e method. We find typical abundances 12+log(O/H) = 7.9 ($\sim$0.2 times the solar value) and an evolution of 0.9$\pm$0.5 dex in oxygen abundance at fixed stellar mass from z$\simeq$8 to 0. These results are compatible with theoretical predictions, albeit with large (conservative) uncertainties in both mass and metallicity. We assess both statistical and systematic uncertainties to identify promising means of improvement with the Atacama Large Millimeter Array (ALMA) and the James Webb Space Telescope (JWST). In particular we highlight [O III] 52$\mu$m as a valuable feature for robust metallicity measurements. Precision of 0.1-0.2 dex in T_e-based O/H abundance can be reasonably achieved for galaxies at z$\approx$5-8 by combining [O III] 52$\mu$m with rest-frame optical strong lines. It will also be possible to probe gas mixing and mergers via resolved T_e-based abundances on kpc scales. With ALMA and JWST, direct metallicity measurements will thus be remarkably accessible in the reionization epoch.Comment: 12 pages, 3 figures, 4 tables. Accepted for publication in Ap

Outflows in Star-forming Galaxies: Stacking Analyses of Resolved Winds and the Relation to Their Hosts' Properties

Outflows form an integral component in regulating the gas cycling in and out of galaxies, although their impact on the galaxy hosts is still poorly understood. Here we present an analysis of 405 high mass (log M$_{*}$/M$_{\odot}\geqslant10$), star-forming galaxies (excluding AGN) with low inclinations at $z\sim$0, using stacking techniques of the NaD $\lambda\lambda$5889,5895 A neutral gas tracer in IFU observations from the MaNGA DR15 survey. We detect outflows in the central regions of 78/405 galaxies and determine their extent and power through the construction of stacked annuli. We find outflows are most powerful in central regions and extend out to $\sim$1R$_{e}$, with declining mass outflow rates and loading factors as a function of radius. The stacking of spaxels over key galaxy quantities reveals outflow detections in regions of high $\Sigma_{\text{SFR}}$ ($\gtrsim$0.01 M$_{\odot}$yr$^{-1}$kpc$^{-2}$) and $\Sigma_{M_{*}}$ ($\gtrsim$10$^{7}$ M$_{\odot}$kpc$^{-2}$) along the resolved main sequence. Clear correlations with $\Sigma_{\text{SFR}}$ suggest it is the main regulator of outflows, with a critical threshold of $\sim$0.01 M$_{\odot}$yr$^{-1}$kpc$^{-2}$ needed to escape the weight of the disk and launch them. Furthermore, measurements of the H$\delta$ and D$_{n}$4000 indices reveal virtually identical star formation histories between galaxies with outflows and those without. Finally, through stacking of HI 21 cm observations for a subset of our sample, we find outflow galaxies show reduced HI gas fractions at central velocities compared to their non-detection control counterparts, suggestive of some removal of HI gas, likely in the central regions of the galaxies, but not enough to completely quench the host.Comment: 20 pages, 11 figures. Accepted for publication in MNRA

Nature and Nurture? Comparing Lyα Detections in UV-bright and Fainter [O iii]+Hβ Emitters at z ∼ 8 with Keck/MOSFIRE

The 100% detection rate of Lyα emission in a sample of four luminous z ∼ 8 galaxies with red Spitzer/IRAC colors suggests objects with unusual ionizing capabilities that created early ionized bubbles in a neutral era. Whether such bubbles reflect enhanced ionizing properties (nature) or an overdense environment (nurture), however, remains unclear. Here we aim to distinguish between these hypotheses via a search for Lyα emission in five fainter galaxies drawn from the CANDELS-GOODS fields using a similar IRAC excess and UV magnitudes that should reflect reduced clustering effects. Using Keck/MOSFIRE we tentatively detect >4σ line emission in only two targets at redshifts z_{Lyα} = 7.1081 and 7.9622 with rest-frame EWs of 16–17 Å, ∼1.5× weaker compared to their brighter counterparts. Thus, we find a reduced rate for Lyα emission of 0.40_{-0.25}^{+0.30} compared to 1.00_{-0.44}^{+0.00} for more luminous examples. The lower rate agrees with predictions from simulations of a mostly neutral intergalactic medium and an intrinsic EW0,Lyα distribution for z ∼ 6 galaxies. However, even with an extreme EW_{0,Lyα} model, it is challenging to match the detection rate for the luminous objects. Spectral energy distribution fitting of our fainter sample indicates young and star-forming systems, albeit with less extreme star formation rates and ionization parameters compared to their luminous counterparts. The enhanced Lyα rate in luminous galaxies is thus likely a byproduct of both extreme ionizing properties as well as environmental effects. Further studies with JWST may be required to resolve the physical nature of this puzzling population

Lyman α Emission from a Luminous z = 8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization

We report the discovery of Lyman-alpha emission (Lyα) in the bright galaxy EGSY-2008532660 (hereafter EGSY8p7) using the Multi-Object Spectrometer For Infra-Red Exploration spectrograph at the Keck Observatory. First reported by Roberts-Borsani et al., this galaxy was selected for spectroscopic observations because of its photometric redshift (z_(phot) =(8.57)_(-0.43)^{+0.22)), apparent brightness (H_(160) = 25.26 ± 0.09$), and red Spitzer/IRAC [3.6]–[4.5] color indicative of contamination by strong oxygen emission in the [4.5] band. With a total integration of ~4.3 hr, our data reveal an emission line at ≃11776 Å that we argue is likely Lyα at a redshift of z_(spec) = {8.683}_(-0.004)^(+0.001), in good agreement with the photometric estimate. The line was detected independently on two nights using different slit orientations and its detection significance is ~ 7.5σ. An overlapping skyline contributes significantly to the uncertainty on the total line flux, although the significance of the detected line is robust to a variety of skyline-masking procedures. By direct addition and a Gaussian fit, we estimate a 95% confidence range of 1.0–2.5 × 10^(−17) erg s^(−1) cm^(−2), corresponding to a rest-frame equivalent width of 17–42 Å. EGSY8p7 is the most distant spectroscopically confirmed galaxy to date, and the third luminous source in the EGS field beyond z_(phot) ≳ 7.5 with detectable Lyα emission, viewed at a time when the intergalactic medium is believed to be fairly neutral. Although the reionization process was probably patchy, we discuss whether luminous sources with prominent IRAC color excesses may harbor harder ionizing spectra than the dominant fainter population, thereby creating earlier ionized bubbles. Further spectroscopic follow-up of such bright sources promises important insights into the early formation of galaxies

The Super Eight Galaxies: Properties of a Sample of Very Bright Galaxies at 7 \u3c z \u3c 8

We present the Super Eight galaxies - a set of very luminous, high-redshift (7.1 \u3c z \u3c 8.0) galaxy candidates found in the Brightest of Reionizing Galaxies (BoRG) Survey fields. The original sample includes eight galaxies that are Y-band dropout objects with H-band magnitudes of m H \u3c 25.5. Four of these objects were originally reported in Calvi et al. Combining new Hubble Space Telescope (HST) WFC3/F814W imaging and Spitzer IRAC data with archival imaging from BoRG and other surveys, we explore the properties of these galaxies. Photometric redshift fitting places six of these galaxies in the redshift range of 7.1 \u3c z \u3c 8.0, resulting in three new high-redshift galaxies and confirming three of the four high-redshift galaxy candidates from Calvi et al. We calculate the half-light radii of the Super Eight galaxies using the HST F160W filter and find that the Super Eight sizes are in line with the typical evolution of size with redshift. The Super Eights have a mean mass of log (M ∗/M o) ∼10, which is typical for sources in this luminosity range. Finally, we place our sample on the UV z ∼ 8 luminosity function and find that the Super Eight number density is consistent with other surveys in this magnitude and redshift range