The detection of two $z\sim 13$ galaxy candidates has opened a new window on galaxy formation at an era only $330$ Myr after the Big Bang. Here, we investigate the physical nature of these sources: are we witnessing star forming galaxies or quasars at such early epochs? If powered by star formation, the observed ultraviolet (UV) luminosities and number densities can be jointly explained if: (i) these galaxies are extreme star-formers with star formation rates $5-24\times$ higher than those expected from extrapolations of average lower-redshift relations; (ii) the star formation efficiency increases with halo mass and is countered by increasing dust attenuation from $z \sim 10-5$; (iii) they form stars with an extremely top-heavy initial mass function. The quasar hypothesis is also plausible, with the UV luminosity produced by black holes of $\sim 10^8 \, \mathrm{M_{\odot}}$ accreting at or slightly above the Eddington rate ($f_{\rm Edd}\sim 1.0$). This black hole mass at $z\sim13$ would require very challenging, but not implausible, growth parameters. If spectroscopically confirmed, these two sources will represent a remarkable laboratory to study the Universe at previously inaccessible redshifts.
A tidal disruption event (TDE) occurs when a star is destroyed by the strong tidal shear of a massive black hole (MBH). The accumulation of TDE observations over the last years has revealed that post-starburst galaxies are significantly overrepresented in the sample of TDE hosts. Here we address the post-starburst preference by investigating the decline of TDE rates in a Milky-Way like nuclear stellar cluster featuring either a monochromatic (1 M$\odot$) or a complete, evolved stellar mass function. In the former case, the decline of TDE rates with time is very mild, and generally up to a fact…
We present the results of our systematic search for the reddest far-infrared (FIR) and submillimeter (sub-mm) galaxies using the data from the Herschel Multi-tiered Extragalactic Survey (HerMES) and the SCUBA2 Cosmological Legacy Survey (S2CLS). The red FIR galaxies are "500~$μ$m risers," whose spectral energy distributions increase with wavelength across the three FIR passbands of the Spectral and Photometric Imaging REceiver (SPIRE) of Herschel. Within 106.5 deg$^2$ of the HerMES fields, we have selected 629 500 $μ$m risers. The red sub-mm galaxies are "SPIRE dropouts," which are prominent d…
We report the discovery of an optical Einstein Ring in the Sculptor constellation, IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is an almost complete ring ($\sim 300^{\circ}$) with a diameter of $\sim 4.5\, {\rm arcsec}$. The discovery was made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging data. Confirmation of the object nature has been obtained by deriving spectroscopic redshifts for both components, lens and source, from observations at the $10.4$ m Gran Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massiv…
Starbursts and substantial variations in the star formation histories are a common phenomenon in galaxies. We study the stability properties of isolated star-forming dwarf galaxies with the aim of identifying starburst modes. The impact of the stellar birth function, the initial mass function (IMF), the stellar feedback and the interstellar medium (ISM) model are investigated. We apply a one-zone model for a star-gas system coupled by mass and energy transfer. Additionally, we extend the network for active dynamical evolution. This allows for a coupling between the dynamical state of the galax…
Using the IRAM 30-m telescope, CN and CO isotopologues have been measured toward the central regions of the nearby starburst galaxy NGC253 and the prototypical ultraluminous infrared galaxy Mrk231. In NGC253, the 12C/13C ratio is 40+-10. Assuming that the ratio also holds for the CO emitting gas, this yields 16O/18O = 145+-36 and 16O/17O = 1290+-365 and a 32S/34S ratio close to that measured for the local interstellar medium (20-25). No indication for vibrationally excited CN is found. Peak line intensity ratios between NGC253 and Mrk231 are ~100 for 12C16O and 12C18O J=1-0, while the ratio fo…
(abridged) We used HST/ACS to obtain deep V- and I-band images of NGC 1569, one of the closest and strongest starburst galaxies in the Universe. These data allowed us to study the underlying old stellar population, aimed at understanding NGC 1569's evolution over a full Hubble time. We focus on the less-crowded outer region of the galaxy, for which the color-magnitude diagram (CMD) shows predominantly a red giant branch (RGB) that reaches down to the red clump/horizontal branch feature (RC/HB). A simple stellar population analysis gives clear evidence for a more complicated star formation hist…
Accretion of gas from the cosmic web to galaxy halos and ultimately their disks is a prediction of modern cosmological models but is rarely observed directly or at the full rate expected from star formation. Here we illustrate possible large-scale cosmic HI accretion onto the nearby dwarf starburst galaxy IC10, observed with the VLA and GBT. We also suggest that cosmic accretion is the origin of sharp metallicity drops in the starburst regions of other dwarf galaxies, as observed with the 10-m GTC. Finally, we question the importance of cosmic accretion in normal dwarf irregulars, for which a …
We present the discovery of a low-redshift damped Ly$α$ (DLA) system in the spectrum of background starburst galaxy SDSS J111323.88+293039.3 ($z=0.17514$). The DLA is at an impact parameter of $\rm ρ=36~kpc$ from the star forming galaxy, SDSS J111324.08+293051.2 ($z=0.17077$). We measure an HI column density of $N($HI$)\rm =3.47\times10^{20}~cm^{-2}$ along with multiple low-ionization species such as NI, NII, SiII, CII, and SiIII. We also make an estimate of the covering fraction to be 0.883, giving us a limiting size of the DLA to be $A_{DLA}\rm \geq3.3~kpc^2$. Assuming a uniform column densi…
We present James Webb Space Telescope (JWST) imaging of NGC 7469 with the Near-Infrared Camera (NIRCam) and the Mid-InfraRed Instrument (MIRI). NGC 7469 is a nearby, $z=0.01627$, luminous infrared galaxy (LIRG) that hosts both a Seyfert Type-1.5 nucleus and a circumnuclear starburst ring with a radius of $\sim$0.5 kpc. The new near-infrared (NIR) JWST imaging reveals 66 star-forming regions, 37 of which were not detected by HST observations. Twenty-eight of the 37 sources have very red NIR colors that indicate obscurations up to A$_{\rm{v}}\sim7$ and a contribution of at least 25$\%$ from hot …
One way the AGN are expected to influence the evolution of their host galaxies is by removing metal content via outflows. In this article we present results that show that AGN can have an effect on the chemical enrichment of their host galaxies using the fossil record technique on CALIFA galaxies. We classified the chemical enrichment histories of all galaxies in our sample regarding whether they show a drop in the value of their metallicity. We find that galaxies currently hosting an AGN are more likely to show this drop in their metal content compared to the quiescent sample. Once we separat…
We report the discovery of two companion sources to a strongly lensed galaxy SPT0418-47 ("ring") at redshift 4.225, targeted by the JWST Early Release Science program. We confirm that these sources are at a similar redshift as the ring based on H$α$ detected in the NIRSpec spectrum, and [C II] 158 $μ$m line from ALMA. Using multiple spectral lines detected in JWST/NIRSpec, the rest-frame optical to infrared images from NIRCam and MIRI, and far-infrared (FIR) dust continuum detected by ALMA, we argue that the newly discovered sources are actually lensed images of the same companion galaxy, here…
Far-infrared and submillimeter wavelength surveys have now established the important role of dusty, star-forming galaxies (DSFGs) in the assembly of stellar mass and the evolution of massive galaxies in the Universe. The brightest of these galaxies have infrared luminosities in excess of 10$^{13}$ L$_{\odot}$ with implied star-formation rates of thousands of solar masses per year. They represent the most intense starbursts in the Universe, yet many are completely optically obscured. Their easy detection at submm wavelengths is due to dust heated by ultraviolet radiation of newly forming stars.…
We present a near-infrared study of the candidate star cluster Mercer 81, located at the centre of the G338.4+0.1 HII region, and close to the TeV gamma-ray source HESS 1640-465. Using HST/NICMOS imaging and VLT/ISAAC spectroscopy we have detected a compact and highly extincted cluster of stars, though the bright stars in the centre of the field are in fact foreground objects. The cluster contains nine stars with strong Paschen-alpha emission, one of which we identify as a Wolf-Rayet (WR) star, as well as an A-type supergiant. The line-of-sight extinction is very large, $A_{V}\sim 45$, illustr…
We present an analysis of the structures, sizes, star formation rates, and local environmental properties of galaxies at z~4-6, utilising deep Hubble Space Telescope imaging of the Hubble Ultra Deep Field. The galaxies we study are selected with the Lyman-break drop-out technique, using galaxies which are B-,V-, and i-drops, which effectively selects UV bright starbursting galaxies between z=4 and z=6. Our primary observational finding is that starbursting galaxies at z>4 have a diversity in structure, with roughly 30% appearing distorted and asymmetric, while the majority are smooth and appar…
In the Milky Way, cosmic rays (CRs) are dynamically important in the interstellar medium, contribute to hydrostatic balance, and may help regulate star formation. However, we know far less about the importance of CRs in galaxies whose gas content or star formation rate differ significantly from those of the Milky Way. Here we construct self-consistent models for hadronic CR transport, losses, and contribution to pressure balance as a function of galaxy properties, covering a broad range of parameters from dwarfs to extreme starbursts. While the CR energy density increases from $\sim 1$ eV cm$^…
Observations of the molecular gas over scales of 0.5 to several kpc provide crucial information on how gas moves through galaxies, especially in mergers and interacting systems, where it ultimately reaches the galaxy center, accumulates, and feeds nuclear activity. Studying the processes involved in the gas transport is an important step forward to understand galaxy evolution. 12CO, 13CO and C18O1-0 high-sensitivity ALMA observations were used to assess properties of the large-scale molecular gas reservoir and its connection to the circumnuclear molecular ring in NGC1614. The role of excitatio…
We performed a series of 29 gasdynamical simulations of disc galaxies, barred and unbarred, with various stellar masses, to study the impact of the bar on star formation history. Unbarred galaxies evolve very smoothly, with a star formation rate (SFR) that varies by at most a factor of three over a period of 2 Gyr. The evolution of barred galaxies is much more irregular, especially at high stellar masses. In these galaxies, the bar drives a substantial amount of gas toward the centre, resulting in a high SFR, and producing a starburst in the most massive galaxies. Most of the gas is converted …
[abridged] Building upon a previous study, we define a method to blindly identify galaxies that underwent, and may still be undergoing, a fast downfall of their star-formation activity, that is, a more than 80% drop in star-formation rate (SFR) occurring in less than 500 Myr. Modeling galaxies' SED with a delayed-$τ$ star formation history (SFH), with and without allowing an instantaneous SFR drop within the last hundreds Myr, we isolate 102 candidates out of a subsample of 6,680 galaxies classified as star-forming from the UVJ criterion in the ZFOURGE catalogues. These galaxies are mostly loc…
Lyman Break Galaxy (LBG) candidates at z>10 are rapidly being identified in JWST/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts (z<7) may also mimic the near-infrared (near-IR) colors of z>10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150…
We used multi-wavelength analysis of the newly observed molecular gas (12CO and 13CO (1-0)) with interferometer CARMA and archival star formation tracers to constrain the interaction, merging, and star formation history of an off-center minor merger, a three-spiral barred galaxy NGC 5430 and its satellite embedded in the bar. Morphology of the molecular gas in the bar of NGC 5430 shows minimal signs of recent interactions in our resolution. The apparent morphological remnant of the past galaxy interaction is an asymmetric spiral arm, containing more molecular gas and exhibiting higher star for…
Compact starburst galaxies are thought to include many or most of the galaxies from which substantial Lyman continuum emission can escape into the intergalactic medium. Li and Malkan (2018) used SDSS photometry to find a population of such starburst galaxies at z~0.5. They were discovered by their extremely strong [OIII]4959+5007 emission lines, which produce a clearly detectable excess brightness in the i bandpass, compared with surrounding filters. We therefore used the HST/COS spectrograph to observe two of the newly discovered i-band excess galaxies around their Lyman limits. One has stron…
Quasars are the most luminous of active galactic nuclei (AGN), and are perhaps responsible for quenching star formation in their hosts. The Stripe 82X catalog covers 31.3 deg$^2$ of the Stripe 82 field, of which the 15.6 deg$^2$ covered with XMM-Newton is also covered by Herschel/SPIRE. We have 2500 X-ray detected sources with multi-wavelength counterparts, and 30% of these are unobscured quasars, with $L_X > 10^{44}\,$erg/s and $M_B < -23$. We define a new population of quasars which are unobscured, have X-ray luminosities in excess of $10^{44}\,$erg/s, have broad emission lines, and yet are …
We study the effects of the environment on galaxy quenching in the outskirts of clusters at $0.04 < z < 0.08$. We use a subsample of 14 WINGS and OmegaWINGS clusters that are linked to other groups/clusters by filaments and study separately galaxies located in two regions in the outskirts of these clusters according to whether they are located towards the filaments' directions or not. We also use samples of galaxies in clusters and field as comparison. Filamentary structures linking galaxy groups/clusters were identified over the Six Degree Field Galaxy Redshift Survey Data Release 3. We find …
Motivated by the discovery of the ultra-strong emission line starburst galaxies (EELGs) known as "green pea galaxies", we consider here their contribution to the intergalactic flux of ionizing UV at high redshifts. Most galaxies that have been observed show a precipitous drop in their flux blueward of the Lyman limit. However, recent observations of EELGs have discovered that many more Lyman continuum photons escape from them into intergalactic space than was previously suspected. We calculate their contribution to the extragalactic background light (EBL). We also calculate the effect of these…
We present here spatially-resolved optical spectroscopic observations of four nearby dwarf Wolf-Rayet (WR) galaxies. The ages of the most recent starburst events in these galaxies are found between 3 and 10 Myr. The gas-phase metallicities [12+log(O/H)] for the spatially-resolved star-forming regions are derived using several indicators. The star-forming regions within the galaxies are found chemically homogeneous within the uncertainties in the estimates. Nitrogen-enrichment as expected in the WR regions is not detected. This implies that metal-enrichment due to supernovae explosions in the m…
We present results from sensitive, multi-epoch NuSTAR observations of the late-type star-forming galaxy M83 (d=4.6 Mpc), which is the first investigation to spatially resolve the hard (E>10 keV) X-ray emission of this galaxy. The nuclear region and ~ 20 off-nuclear point sources, including a previously discovered ultraluminous X-ray (ULX) source, are detected in our NuSTAR observations. The X-ray hardnesses and luminosities of the majority of the point sources are consistent with hard X-ray sources resolved in the starburst galaxy NGC 253. We infer that the hard X-ray emission is most likely d…
The rate of star formation both in the Galaxy and in external galaxies should be related to the physical properties of the molecular clouds from which stars form. This is expected for the starbursts found both in irregular galaxies and in some mergers. The dwarf galaxy Henize 2-10 is particularly interesting in this context as it shows a number of newly formed Super Star Clusters (SSCs) associated with a very rich molecular environment. We present a high angular resolution study of the molecular gas associated with the SSCs with the aim of deriving the physical properties of the parent molecul…
Molecular hydrogen is the most abundant molecular species in the Universe. While no doubts exist that it is mainly formed on the interstellar dust grain surfaces, many details of this process remain poorly known. In this work, we focus on the fate of the energy released by the H$_2$ formation on the dust icy mantles, how it is partitioned between the substrate and the newly formed H$_2$, a process that has a profound impact on the interstellar medium. We carried out state-of-art \textit{ab-initio} molecular dynamics simulations of H$_2$ formation on periodic crystalline and amorphous ice surfa…
