We present 2D-spectroscopic observations from Centro Astronómico Hispano Alemán (CAHA) 3.5 m telescope and the millimetre observation from NOrthern Extended Millimeter Array (NOEMA) of the nearby S0 galaxy PGC 26218, which shows central star-formation activity and post-starburst outside in the disk. We estimate the star formation rate (SFR = $0.28\pm0.01$ $M_{\odot} \rm yr^{-1}$) and molecular gas mass ($\rm log\ $$M_{\rm H_{2}}=7.60\pm0.15\ M_{\odot}$) of PGC 26218 based on the extinction-corrected H$α$ emission line and the CO-$\rm H_{2}$ conversion factor ($α_{\rm CO}$) of the Milky Way, respectively. We find that PGC 26218 follows the star forming main sequence (SFMS) and the Kennicutt-Schmidt law. Comparing the kinematics of CO($J$=1-0), stars and H$α$, we find that the rotational axis of CO($J$=1-0) is 45$^{\circ}$ different from that of H$α$. In addition, the profile of the CO($J$=1-0) emission line shows asymmetry and has an inflow component of $\sim$ 46 $\rm km\ s^{-1}$. With the decomposition of the optical image, we confirm that PGC 26218 shows multiple nuclear structures. The projected offset between the most luminous optical center and the center of CO($J$=1-0) is $5.2\arcsec$ ($\sim$ 0.6 kpc) and the latter overlaps with one of the optical cores. These results support that PGC 26218 may have experienced a gas-rich minor merger, extending its star formation and locating it in the SFMS.
We present MUSE integral field spectroscopic observations of the host galaxy (PGC 043234) of one of the closest ($z=0.0206$, $D\simeq 90$ Mpc) and best-studied tidal disruption events (TDE), ASASSN-14li. The MUSE integral field data reveal asymmetric and filamentary structures that extend up to $\gtrsim 10$ kpc from the post-starburst host galaxy of ASASSN-14li. The structures are traced only through the strong nebular [O III] $λ$5007, [N II] $λ$6584, and H$α$ emission lines. The total off nuclear [O III] $λ$5007 luminosity is luminosity is $4.7\times 10^{39}$ erg s$^{-1}$ and the ionized H ma…
We present a photometric study of PGC 1000714, a galaxy resembling Hoag's Object with a complete detached outer ring, that has not yet been described in the literature. Since the Hoag-type galaxies are extremely rare and peculiar systems, it is necessary to increase the sample of known objects by performing the detailed studies on the possible candidates to derive conclusions about their nature, evolution, and systematic properties. We therefore performed surface photometry of the central body by using the archival near-UV, infrared data and the new optical data (BVRI). This current work has r…
Post-starburst galaxies can be identified via the presence of prominent Hydrogen Balmer absorption lines in their spectra. We present a comprehensive study of the origin of strong Balmer lines in a volume-limited sample of 189 galaxies with $0.01<z<0.05$, $\log(\mbox{M}_{\star}/\mbox{M}_{\odot})>9.5$ and projected axis ratio $b/a>0.32$. We explore their structural properties, environments, emission lines and star formation histories, and compare them to control samples of star-forming and quiescent galaxies, and simulated galaxy mergers. Excluding contaminants, in which the strong Balmer lines…
We test models of starburst driven outflows using observations of the 22.2 GHz H$_2$O and 36.2 GHz class I CH$_3$OH maser lines. We have observed the starburst galaxy NGC 253 using the Karl G. Jansky Very Large Array. We present evidence for entrainment of star-forming dense-molecular gas in the outflow of NGC 253. We also show that H$_2$O masers are associated with forming super star clusters and not with supernova remnants. We detect four new 36 GHz CH$_3$OH masers in the central kpc and show possible evidence for a star-formation origin of two class I CH$_3$OH masers. Such high resolution o…
Recent observations have revealed that starburst galaxies can drive molecular gas outflows through stellar radiation pressure. Molecular gas is the phase of the interstellar medium from which stars form, so these outflows curtail stellar mass growth in galaxies. Previously known outflows, however, involve small fractions of the total molecular gas content and are restricted to sub-kiloparsec scales. It is also apparent that input from active galactic nuclei is in at least some cases dynamically important, so pure stellar feedback has been considered incapable of aggressively terminating star f…
Nuclear starburst discs (NSDs) are very compact star-forming regions in the centers of galaxies that have been studied as a possible origin for the absorbing gas around a central active galactic nucleus. NSDs may be most relevant at $z\sim 1$ when obscured accretion onto supermassive black holes (SMBHs) is common. This paper describes the characteristics of the stellar remnants of NSDs at $z=0.01$, taking into account the evolution from $z=1$. Using a stellar synthesis model, the colours, masses, and luminosities of the stellar remnants are computed for a suite of 192 two-dimensional NSD model…
We report on the detection of Lyman continuum radiation in two nearby starburst galaxies. Tol 0440-381, Tol 1247-232 and Mrk 54 were observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescopes. The three galaxies have radial velocities of ~13,000 km/s, permitting a ~35 A window on the restframe Lyman continuum shortward of the Milky Way Lyman edge at 912 A. The chosen instrument configuration using the G140L grating covers the spectral range from 912 to 2,000 Å. We developed a dedicated background subtraction method to account for temporal and spatial background variation…
We present a study of 7 star-forming galaxies from the Cosmic Evolution Survey (COSMOS) observed with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope (HST). The galaxies are located at relatively low redshifts, $z\sim$0.3, with morphologies ranging from extended and disturbed to compact and smooth. To complement the HST observations we also analyze observations taken with the VIMOS spectrograph on the Very Large Telescope (VLT). In our galaxy sample we identify three objects with double peak Lyman-$α$ profiles similar to those seen in Green Pea compact galaxies and me…
We introduce the `Illustris zoom simulation project', which allows the study of selected galaxies forming in the $Λ$CDM cosmology with a 40 times better mass resolution than in the parent large-scale hydrodynamical Illustris simulation. We here focus on the starburst properties of the gas in four cosmological simulations of major mergers. The galaxies in our high-resolution zoom runs exhibit a bursty mode of star formation with gas consumption timescales 10 times shorter than for the normal star formation mode. The strong bursts are only present in the simulations with the highest resolution, …
In this study we present the exploration of $\sim$500 spectroscopically confirmed galaxies in and around two large scale structures at $z\sim1$ drawn from the ORELSE survey. A sub-sample of these galaxies ($\sim$150) were targeted for the initial phases of a near-infrared MOSFIRE spectroscopic campaign investigating the differences in selections of galaxies which had recently ended a burst of star formation or had rapidly quenched (i.e., post-starburst or K+A galaxies). Selection with MOSFIRE resulted in a post-starburst sample more than double that selected by traditional $z\sim1$ (observed-f…
Context. The fraction of field binaries on retrograde orbits about the Milky Way is significantly lower compared to its prograde counterpart. Chemical and dynamical evidence suggests that the retrograde stellar population originates from $ω$ Centauri, which is either the most massive globular cluster (GC) of the Milky Way or the putative core of a former dwarf galaxy. Aims. Star formation conditions required to produce the retrograde binary population are constrained assuming that the retrograde stellar population originates from $ω$ Centauri's progenitor. Methods. We match the observed low bi…
We present [CII] synthetic observations of smoothed particle hydrodynamics (SPH) simulations of a dwarf galaxy merger. The merging process varies the star-formation rate by more than three orders of magnitude. Several star clusters are formed, the feedback of which disperses and unbinds the dense gas through expanding HII regions and supernova (SN) explosions. For galaxies with properties similar to the modelled ones, we find that the [CII] emission remains optically thin throughout the merging process. We identify the Warm Neutral Medium ($3<\log T_{\rm gas}<4$ with $χ_{\rm HI}>2χ_{\rm H2}$) …
We discuss the possible origin of the double-peaked profiles recently observed in Lyman-Alpha Emitters (LAEs) at the epoch of reionization ($z \gtrsim 6.5$) from obscured active galactic nuclei (AGN). Combining the extent of the Lyman-$α$ near-zones estimated from the blue peak velocity offset in these galaxies, with the ionizing emissivity of quasars at $z \gtrsim 6$, we forecast the intrinsic UV and X-ray luminosities of the AGN needed to give rise to their double-peaked profiles. We also estimate the extent of the obscuration of the AGN by comparing their luminosities to those of similar qu…
We report on observations made with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) using background QSOs to probe the circum-galactic medium (CGM) around 17 low-redshift galaxies that are undergoing or have recently undergone a strong starburst (the COS-Burst program). The sightlines extend out to roughly the virial radius of the galaxy halo. We construct control samples of normal star-forming low-redshift galaxies from the COS/HST archive that match the starbursts in terms of galaxy stellar mass and impact parameter. We find clear evidence that the CGM around the st…
The role of starburst winds versus active galactic nuclei (AGN) jets/winds in the formation of the kiloparsec scale radio emission seen in Seyferts is not yet well understood. In order to be able to disentangle the role of various components, we have observed a sample of Seyfert galaxies exhibiting kpc-scale radio emission suggesting outflows, along with a comparison sample of starburst galaxies, with the EVLA B-array in polarimetric mode at 1.4 GHz and 5~GHz. Polarization is clearly detected in three Seyfert galaxies and one starburst galaxy. The Seyfert galaxy NGC\,2639, shows highly polariz…
We mapped 3 mm continuum and line emission from the starburst galaxy M82 using the Combined Array for Research in Millimeter-wave Astronomy. We targeted the HCN, HCO$^{+}$, HNC, CS and HC$_{3}$N lines, but here we focus on the HCN and HCO$^{+}$ emission. The map covers a field of 1.2' with a ~5" resolution. The HCN and HCO$^{+}$ observations are combined with single dish images. The molecular gas in M82 had been previously found to be distributed in a molecular disk, coincident with the central starburst, and a galactic scale outflow which originates in the central starburst. With the new shor…
We present the evolution in the number density and stellar mass functions of photometrically selected post-starburst galaxies in the UKIDSS Deep Survey (UDS), with redshifts of 0.5<z<2 and stellar masses logM>10. We find that this transitionary species of galaxy is rare at all redshifts, contributing ~5% of the total population at z~2, to <1% by z~0.5. By comparing the mass functions of quiescent galaxies to post-starburst galaxies at three cosmic epochs, we show that rapid quenching of star formation can account for 100% of quiescent galaxy formation, if the post-starburst spectral features a…
While the formation of stellar clumps in distant galaxies is usually attributed to gravitational violent disk instabilities, we show here that major mergers also represent a competitive mechanism to form bright clumps. Using ~0.1'' resolution ACS F814W images in the entire COSMOS field, we measure the fraction of clumpy emission in 109 main sequence (MS) and 79 Herschel-detected starbursts (off-MS) galaxies at 0.5 < z < 0.9, representative of normal versus merger induced star-forming activity, respectively. We additionally identify merger samples from visual inspection and from Gini-M20 morpho…
We present a detailed study of a molecular outflow feature in the nearby starburst galaxy NGC 253 using ALMA. We find that this feature is clearly associated with the edge of NGC 253's prominent ionized outflow, has a projected length of ~300 pc, with a width of ~50 pc and a velocity dispersion of ~40 km s^-1, consistent with an ejection from the disk about 1 Myr ago. The kinematics of the molecular gas in this feature can be interpreted (albeit not uniquely) as accelerating at a rate of 1 km s^-1 pc^-1. In this scenario, the gas is approaching escape velocity at the last measured point. Strik…
The question how much star formation is occurring at low metallicity throughout the cosmic history appears crucial for the discussion of the origin of various energetic transients, and possibly - double black hole mergers. We revisit the observation-based distribution of birth metallicities of stars (f$_{\rm SFR}$(Z,z)), focusing on several factors that strongly affect its low metallicity part: (i) the method used to describe the metallicity distribution of galaxies (redshift-dependent mass metallicity relation - MZR, or redshift-invariant fundamental metallicity relation - FMR), (ii) the cont…
We present a chemodynamical analysis of 11,562 metal-rich, high-eccentricity halo-like main-sequence (MS) stars, which has been referred to as the Splash or Splashed Disk, selected from Sloan Digital Sky Survey (SDSS) and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). When divided into two groups, a low-[$α$/Fe] population (LAP) and a high-[$α$/Fe] population (HAP), based on kinematics and chemistry, we find that they exhibit very distinct properties, indicative of different origins. From a detailed analysis of their orbital inclinations, we suggest that the HAP arises fro…
Optically-compact star-forming galaxies (SFGs) have been proposed as immediate progenitors of quiescent galaxies, although their origin and nature are debated. Were they formed in slow secular processes or in rapid merger-driven starbursts? Addressing this question would provide fundamental insight into how quenching occurs. We explore the location of the general population of galaxies with respect to fundamental star-forming and structural relations, identify compact SFGs based on their stellar core densities, and study three diagnostics of the burstiness of star formation: 1) Star formation …
About 35 years ago a class of galaxies with unusually strong Balmer absorption lines and weak emission lines was discovered in distant galaxy clusters. These objects, alternatively referred to as post-starburst, E+A or k+a galaxies, are now known to occur in all environments and at all redshifts, with many exhibiting compact morphologies and low-surface brightness features indicative of past galaxy mergers. They are commonly thought to represent galaxies that are transitioning from blue to red sequence, making them critical to our understanding of the origins of galaxy bimodality. However, rec…
Star-forming galaxies have been predicted to contribute considerably to the diffuse gamma-ray background as they are guaranteed reservoirs of cosmic rays. Assuming that the hadronic interactions responsible for high-energy gamma rays also produce high-energy neutrinos and that O(100) PeV cosmic rays can be produced and confined in starburst galaxies, we here discuss the possibility that star-forming galaxies are also the main sources of the high-energy neutrinos observed by the IceCube experiment. First, we compute the diffuse gamma-ray background from star-forming galaxies, adopting the lates…
Submillimeter bright galaxies in the early Universe are vigorously forming stars at ~1000 times higher rate than the Milky Way. A large fraction of stars is formed in the central 1 kiloparsec region, that is comparable in size to massive, quiescent galaxies found at the peak of the cosmic star formation history, and eventually the core of giant elliptical galaxies in the present-day Universe. However, the physical and kinematic properties inside a compact starburst core are poorly understood because dissecting it requires angular resolution even higher than the Hubble Space Telescope can offer…
Revealing the nature of the starburst galaxies in the $z=2.4$ overdensity HATLAS J0849
Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天体物理与天文研究学院）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；DTU Space, Technical University of Denmark（丹麦技术大学空间研究中心）；DARK, Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所DARK中心）；Max-Planck-Institut für Extraterrestrische Physik (MPE)（马克斯·普朗克地外物理学研究所）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study The University of Tokyo（东京大学宇宙起源研究科 Kavli 宇宙物质与物理全球卓越中心）；Sub-department of Astrophysics, Department of Physics, University of Oxford（牛津大学物理系天体物理小组）
The cosmological origin of carbon, the fourth most abundant element in the Universe, is not well known and matter of heavy debate. We investigate the behavior of C/O to O/H in order to constrain the production mechanism of carbon. We measured emission-line intensities in a spectral range from 1600 to 10000 Å on Space Telescope Imaging Spectrograph (STIS) long-slit spectra of 18 starburst galaxies in the local Universe. We determined chemical abundances through traditional nebular analysis and we used a Markov Chain Monte Carlo (MCMC) method to determine where our carbon and oxygen abundances l…
Starbursts hiding in the main sequence: a pathway toward quenching?
Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS UMR 7550（斯特拉斯堡天文台，斯特拉斯堡大学）；University of Strasbourg Institute for Advanced Study（斯特拉斯堡高等研究院）；Laboratoire AIM Paris-Saclay, CEA/IRFU/SAp, Université Paris Diderot（巴黎-萨克雷AIM实验室，CEA/IRFU/SAp，巴黎第七大学）
The star formation rates in starburst galaxies are orders of magnitude higher than in local star-forming regions, and the origin of this difference is not well understood. We use sub-mm spectral line maps to characterize the physical conditions of the molecular gas in the luminous Galactic star-forming region W49A and compare them with the conditions in starburst galaxies. We probe the temperature and density structure of W49A using H_2CO and HCN line ratios over a 2'x2' (6.6x6.6 pc) field with an angular resolution of 15" (~0.8 pc) provided by the JCMT Spectral Legacy Survey. We analyze the r…
To understand the origin of radio emission in radio-quiet AGN and differentiate between the contributions from star formation, AGN accretion, and jets, we have observed a nearby sample of Seyfert galaxies along with a comparison sample of starburst galaxies using the EVLA in full-polarization mode in the B-array configuration. The radio morphologies of the Seyfert galaxies show lobe/bubble-like features or prominent cores in radio emission whereas the starburst galaxies show radio emission spatially coincident with the star-forming regions seen in optical images. There is tentative evidence th…
We present rest-frame optical spectra from the FMOS-COSMOS survey of twelve $z \sim 1.6$ \textit{Herschel} starburst galaxies, with Star Formation Rate (SFR) elevated by $\times$8, on average, above the star-forming Main Sequence (MS). Comparing the H$α$ to IR luminosity ratio and the Balmer Decrement we find that the optically-thin regions of the sources contain on average only $\sim 10$ percent of the total SFR whereas $\sim90$ percent comes from an extremely obscured component which is revealed only by far-IR observations and is optically-thick even in H$α$. We measure the [NII]$_{6583}$/H$…
Keck OSIRIS/LGSAO observations of the ultraluminous galaxy IRAS~23365+3604 resolve a circumnuclear bar (or irregular disk) of semimajor axis 0.42" (520 pc) in Paschen-alpha emission. The line-of-sight velocity of the ionized gas increases from the northeast toward the southwest; this gradient is perpendicular to the photometric major axis of the infrared emission. Two pairs of bends in the zero-velocity line are detected. The inner bend provides evidence for gas inflow onto the circumnuclear disk/bar structure. We interpret the gas kinematics on kiloparsec scales in relation to the molecular g…
Star formation rates (SFR) are compared as determined from mid-infrared 7.7 um PAH luminosity [SFR(PAH)], from 1.4 GHz radio luminosity [SFR(radio)], and from far ultraviolet luminosity [SFR(UV)] for a sample of 287 starburst galaxies with z < 0.5 having Spitzer IRS observations. The previously adopted relation log [SFR(PAH)] = log [vLv(7.7 um)] - 42.57+-0.2, for SFR in solar masses per year and vLv(7.7 um) the luminosity at the peak of the 7.7 um PAH feature in ergs per s, is found to agree with SFR(radio). Comparing with SFR(UV) determined independently from ultraviolet observations of the s…
A candidate accreting massive black hole (BH) with M_BH ~ 10^6 Msun has recently been identified at the center of the dwarf starburst galaxy Henize 2-10 (He 2-10). This discovery offers the first possibility of studying a growing BH in a nearby galaxy resembling those in the earlier universe, and opens up a new class of host galaxies to search for the smallest supermassive BHs. Here we present very long baseline interferometry observations of He 2-10 taken with the Long Baseline Array (LBA) at 1.4 GHz with an angular resolution of ~0.1" x 0.03". A single compact radio source is detected at the…
Starburst galaxies at the peak of cosmic star formation are among the most extreme starforming engines in the universe, producing stars over ~100 Myr. The star formation rates of these galaxies, which exceed 100 $M_\odot$ per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Starburst galaxies are therefore ideal targets to unravel the critical interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH$^+$, is a most useful molecule for such studies because it cannot for…
We obtained optical/near-IR rest-frame Magellan FIRE spectra (including Pa$β$ and Pa$γ$) of 25 starburst galaxies at 0.5<z<0.9, with average star formation rates (SFR) x7 above the Main Sequence (MS). We find that Paschen-to-Balmer line ratios saturate around a constant value corresponding to $A_{\rm V}\sim$2-3 mag, while line to IR luminosity ratios suggest a large range of more extreme obscurations and appear to be uncorrelated to the former. This behavior is not consistent with standard attenuation laws derived for local and distant galaxies, while being remarkably consistent with observati…
We extend our previous work on the age-chemical abundance structure of the Galactic outer disc to the inner disc (4 < r < 8 kpc) based on the SDSS/APOGEE survey. Different from the outer disc, the inner disc stars exhibit a clear bimodal distribution in the [Mg/Fe]-[Fe/H] plane. While a number of scenarios have been proposed in the literature, it remains challenging to recover this bimodal distribution with theoretical models. To this end, we present a chemical evolution model embedding a complex multi-phase inner disc formation scenario that matches the observed bimodal [Mg/Fe]-[Fe/H] distrib…
The ALMA-IMF Large Program observed the W43-MM2-MM3 ridge, whose 1.3mm and 3mm ALMA 12m array continuum images reach a 2500au spatial resolution. We used both the best-sensitivity and the line-free ALMA-IMF images, reduced the noise with the multi-resolution segmentation technique MnGSeg, and derived the most complete and most robust core catalog possible. Using two different extraction software packages, getsf and GExt2D, we identified 200 compact sources, whose 100 common sources have on average fluxes consistent to within 30%. We filtered sources with non-negligible free-free contamination …
We present results from multi-frequency polarization-sensitive Very Large Array observations of the Seyfert-starburst composite galaxy NGC3079. Our sensitive radio observations reveal a plethora of radio filaments comprising the radio lobes in this galaxy. We analyze the origin of these radio filaments in the context of existing Chandra X-ray and HST emission-line data. We do not find a one-to-one correlation of the radio filaments with the emission line filaments. The north-eastern lobe is highly polarized with polarization fractions $\sim$33% at 5 GHz. The magnetic fields are aligned with th…
We present the first spatially resolved study of molecular gas in the vicinity of a Gamma Ray Burst, using CO(2-1) emission line observations with the Atacama Large Millimetre Array (ALMA) at ~50 pc scales. The host galaxy of GRB 980425 contains a ring of high column density HI gas which is likely to have formed due to a collision between the GRB host and its companion galaxy, within which the GRB is located. We detect eleven molecular gas clumps in the galaxy, seven of which are within the gas ring. The clump closest to the GRB position is at a projected separation of ~280 pc. Although it is …
