arXiv subjects

Thiago S. Goncalves

Publications and source records attributed to Thiago S. Goncalves.

5 recordsLinked to original sources

arXiv2025

Highly-ionized gas in lensed z = 6.027 Little Red Dot seen through [OIII] 88$μ$m with ALMA

Determining the physical properties of galaxies during the first billion years after the big bang is key to understanding both early galaxy evolution and how galaxies contributed to the epoch of reionization. We present deep ALMA observations of the redshifted [OIII] 88um line for the gravitationally lensed ($μ= 11.4\pm1.9$) galaxy A383-5.1 (z=6.027) that has previously been detected in [CII] 158um. Recent James Webb Space Telescope (JWST) imaging identified this sub-L* galaxy as a ''Little Red Dot'' (LRD). With a line luminosity of $L_{\rm [OIII]} = (1.29\pm0.24)\times10^8$ L$_\odot$ (corrected for lensing magnification) A383-5.1 is one of the faintest galaxies with combined [CII] and [OIII] detections. The ALMA data reveal no dust continuum emission, consistent with previous observations. The high line luminosity ratio of [OIII]/[CII] $\sim 14\pm5$ is consistent with A383-5.1 being low-metallicity and dust-poor. The non-detection of dust continuum in bands 6 and 8 is consistent with the high [OIII]/[CII] ratio and suggests a presence of a strong ultraviolet radiation field, which would be less affect by dust attenuation, implying that galaxies of this type could contribute significantly to the ionization of the intergalactic medium. The presence of strong ionizing field could provide an important piece of information for understanding the nature of LRDs and their role in cosmic reionization.

astro-ph.GA↗

arXiv2025

Low-redshift analogues of cosmic noon galaxies as laboratories for clumpy star formation

It has been established that a significant fraction of star formation at high-redshift occurs in clumpy galaxies. The properties of clumps and their formation mechanisms, however, remain highly debated. In this work we analyze a sample of 18 Supercompact Ultraviolet Luminous Galaxies observed with the OSIRIS spectrograph at the Keck Telescope, targeting their Pa-alpha emission. These galaxies, although at z~0.1-0.2, share many similar properties with star-forming galaxies at cosmic noon. We find a total of 84 star-forming clumps with typical sizes of a few hundred parsecs. The star-forming clumps exhibit low values of velocity shear (~12 km/s) and high velocity dispersion (~70 km/s). The dynamical masses of the clumps are typically higher than gas masses inferred from the measured star-formation rates of each clump. We also artificially redshift our data to emulate observations at z=2.2 and allow for a direct comparison with other galaxies at higher redshift. Our results indicate that, due to the effects of clump clustering and low-resolution observations, high-z clumps appear larger at greater cosmological distances. This underscores the importance of using low-redshift observations to anchor studies at earlier epochs. Finally, our results support the idea of growing clump sizes in star-forming galaxies as a function of redshift, although not to scales of kpc as found by other works without the benefits of adaptive optics or gravitational lensing.

astro-ph.GA↗

arXiv2013

Evidence for Elevated X-ray Emission in Local Lyman Break Galaxy Analogs

In this paper, we study the relationship between the 2-10 keV X-ray luminosity (L_X), assumed to originate from X-ray binaries (XRBs), and star formation rate (SFR) in UV-selected z<0.1 Lyman break analogs (LBAs). We present Chandra observations for four new GALEX-selected LBAs. Including previously studied LBAs, Haro 11 and VV 114, we find that LBAs demonstrate L_X/SFR ratios that are elevated by ~1.5sigma compared to local galaxies, similar to the ratios found for stacked LBGs in the early Universe (z>2). We show that these LBAs are unlikely to harbor AGN, based on their optical and X-ray spectra and the spatial distribution of the X-rays in three spatially extended cases. We expect that high-mass X-ray binaries (HMXBs) dominate the X-ray emission in these galaxies, based on their high specific SFRs (sSFRs=SFR/M* > 10^{-9}/yr), which suggest the prevalence of young stellar populations. Since both LBAs and LBGs have lower dust attenuations and metallicities compared to similar samples of more typical local galaxies, we investigate the effects of dust extinction and metallicity on the L_X/SFR for the broader population of galaxies with high sSFRs (>10^{-10}/yr). The estimated dust extinctions (corresponding to column densities of N_H<10^{22}/cm^2) are expected to have insignificant effects on observed L_X/SFR ratio for the majority of galaxy samples. We find that the observed relationship between L_X/SFR and metallicity appears consistent with theoretical expectations from X-ray binary population synthesis models. Therefore, we conclude that lower metallicities, related to more luminous HMXBs such as ultraluminous X-ray sources (ULXs), drive the elevated L_X/SFR observed in our sample of z<0.1 LBAs. The relatively metal-poor, active mode of star formation in LBAs and distant z>2 LBGs may yield higher total HMXB luminosity than found in typical galaxies in the local Universe.

astro-ph.CO↗

arXiv2009

An OSIRIS study of the gas kinematics in a sample of UV-selected galaxies: Evidence of "Hot and Bothered" starbursts in the local Universe

We present data from Integral Field Spectroscopy for 3 supercompact UV-Luminous Galaxies (ScUVLGs). As nearby (z~0.2), compact (R_50~1-2 kpc), bright Paschen-alpha sources, with unusually high star formation rates (SFR=3-100 M_sun/yr), ScUVLGs are an ideal population for studying detailed kinematics and dynamics in actively star-forming galaxies. In addition, ScUVLGs appear to be excellent analogs to high redshift Lyman Break Galaxies (LBGs) and our results may offer additional insight into the dynamics of LBGs. Previous work by our team has shown that the morphologies of these galaxies exhibit tidal features and companions, and in this study we find that the dynamics of ScUVLGs are dominated by disturbed kinematics of the emission line gas-- suggestive that these galaxies have undergone recent feedback, interactions or mergers. While 2 of the 3 galaxies do display rotation, v/sigma < 1 -- suggesting dispersion dominated kinematics rather than smooth rotation. We also simulate how these observations would appear at z~2. Lower resolution and loss of low surface brightness features causes some apparent discrepancies between the low-z (observed) and high-z (simulated) interpretations and quantitatively gives different values for v/sigma, yet simulations of these low-z analogs manage to detect the brightest regions well and resemble actual high-z observations of LBGs.

astro-ph.GA↗

arXiv2009

Luminous Thermal Flares from Quiescent Supermassive Black Holes

A dormant supermassive black hole lurking in the center of a galaxy will be revealed when a star passes close enough to be torn apart by tidal forces, and a flare of electromagnetic radiation is emitted when the bound fraction of the stellar debris falls back onto the black hole and is accreted. Here we present the third candidate tidal disruption event discovered in the GALEX Deep Imaging Survey: a 1.6x10^{43} erg s^{-1} UV/optical flare from a star-forming galaxy at z=0.1855. The UV/optical SED during the peak of the flare measured by GALEX and Palomar LFC imaging can be modeled as a single temperature blackbody with T_{bb}=1.7x10^{5} K and a bolometric luminosity of 3x10^{45} erg s^{-1}, assuming an internal extinction with E(B-V)_{gas}=0.3. The Chandra upper limit on the X-ray luminosity during the peak of the flare, L_{X}(2-10 keV)< 10^{41} erg s^{-1}, is 2 orders of magnitude fainter than expected from the ratios of UV to X-ray flux density observed in active galaxies. We compare the light curves and broadband properties of all three tidal disruption candidates discovered by GALEX, and find that (1) the light curves are well fitted by the power-law decline expected for the fallback of debris from a tidally disrupted solar-type star, and (2) the UV/optical SEDs can be attributed to thermal emission from an envelope of debris located at roughly 10 times the tidal disruption radius of a ~10^{7} M_sun central black hole. We use the observed peak absolute optical magnitudes of the flares (-17.5 > M_{g} > -18.9) to predict the detection capabilities of upcoming optical synoptic surveys. (Abridged)

astro-ph.CO↗