We investigate the stellar masses of the class of star-forming objects known as Luminous Compact Blue Galaxies (LCBGs) by studying a sample of galaxies in the distant cluster MS$~$0451.6-0305 at $z\approx0.54$ with ground-based multicolor imaging and spectroscopy. For a sample of 16 spectroscopically-confirmed cluster LCBGs (colour $B-V < 0.5$, surface brightness $μ_B < 21$ mag arcsec$^{-2}$, and magnitude $M_B < -18.5$), we measure stellar masses by fitting spectral energy distribution (SED) models to multiband photometry, and compare with dynamical masses (determined from velocity dispersion between 10 $<$ $σ_v (\rm km~ s^{-1})$ $<$ 80), we previously obtained from their emission-line spectra. We compare two different stellar population models that measure stellar mass in star-bursting galaxies, indicating correlations between the stellar age, extinction, and stellar mass derived from the two different SED models. The stellar masses of cluster LCBGs are distributed similarly to those of field LCBGs, but the cluster LCBGs show lower dynamical-to-stellar mass ratios ($\rm M_{dyn}/M_{\ast} = 2.6$) than their field LCBG counterparts ($\rm M_{dyn}/M_{\ast}=4.8$), echoing trends noted previously in low-redshift dwarf elliptical galaxies. Within this limited sample, the specific star formation rate declines steeply with increasing mass, suggesting that these cluster LCBGs have undergone vigorous star formation.
Luminous Compact Blue Galaxies (LCBGs) are compact, star-forming galaxies that are rarely observed in the local universe but abundant at z=1. This increase in LCBG number density over cosmic lookback time roughly follows the increase in the star formation rate density of the universe over the same period. We use publicly available data in the COSMOS field to study the evolution of the largest homogeneous sample of LCBGs to date by deriving their luminosity function in four redshift bins over the range $0.1\leq~z\leq1$. We find that over this redshift range, the characteristic luminosity (M$^{*…
The luminous blue variable (LBV) stars are peculiar very massive stars. The study of these stellar objects and their surroundings is important for understanding the evolution of massive stars and its effects on the interstellar medium. We study the LBV star candidate G26.47+0.02. Using several large-scale surveys in different frequencies we performed a multiwavelength study of G26.47+0.02 and its surroundings. We found a molecular shell (seen in the 13CO J=1-0 line) that partially surrounds the mid-infrared nebula of G26.47+0.02, which suggests an interaction between the strong stellar winds a…
We present a multiwavelength analysis of the nebula around the candidate luminous blue variable G79.29+0.46. The study is based on our radio observations performed at the Expanded Very Large Array and at the Green Bank Telescope and on archival infrared datasets, including recent images obtained by the Herschel Space Observatory. We confirm that the radio central object is characterized by a stellar wind and derive a current mass-loss rate of about 1.4x10-6 Msun yr-1. We find the presence of a dusty compact envelope close to the star, with a temperature between 40 and 1200 K. We estimate for t…
We study six luminous Lyman-alpha emitters (LAEs) with very blue rest-frame UV continua at $5.7\le z \le 6.6$. These LAEs have previous HST and Spitzer IRAC observations. Combining our newly acquired HST images, we find that their UV-continuum slopes $β$ are in a range of $-3.4\le β\le -2.6$. Unlike previous, tentative detections of $β\simeq -3$ in photometrically selected, low-luminosity galaxies, our LAEs are spectroscopically confirmed and luminous ($M_{\rm UV}<-20$ mag). We model their broadband spectral energy distributions (SEDs), and find that two $β\simeq-2.6\pm0.2$ galaxies can be wel…
We present $HST$ narrow-band near-infrared imaging of Pa$α$ and Pa$β$ emission of 48 local Luminous Infrared Galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey (GOALS). These data allow us to measure the properties of 810 spatially resolved star-forming regions (59 nuclei and 751 extra-nuclear clumps), and directly compare their properties to those found in both local and high-redshift star-forming galaxies. We find that in LIRGs, the star-forming clumps have radii ranging from $\sim90-900$ pc and star formation rates (SFRs) of $\sim1\times10^{-3}$ to 10 M$_\odot$yr$^{-1}$, with…
Luminous Compact Blue Galaxies (LCBGs) are an extreme star-bursting population of galaxies that were far more common at earlier epochs than today. Based on spectroscopic and photometric measurements of LCBGs in massive (M >10^15 M_sun), intermediate redshift (0.5 < z < 0.9) galaxy clusters, we present their rest-frame properties including star-formation rate, dynamical mass, size, luminosity, and metallicity. The appearance of these small, compact galaxies in clusters at intermediate redshift helps explain the observed redshift evolution in the size-luminosity relationship among cluster galaxi…
We present the first results of a high-resolution Karl G. Jansky Very Large Array (VLA) imaging survey of luminous and ultra-luminous infrared galaxies (U/LIRGs) in the Great Observatories All-Sky LIRG Survey (GOALS). From the full sample of 68 galaxies, we have selected 25 LIRGs that show resolved extended emission at sufficient sensitivity to image individual regions of star-formation activity beyond the nucleus.~With wideband radio continuum observations, which sample the frequency range from $3-33$ GHz, we have made extinction-free measurements of the luminosities and spectral indicies for…
We have undertaken a near-infrared spectral survey of stars associated with compact mid-IR shells recently revealed by the MIPSGAL (24 micron) and GLIMPSE (8 micron) Spitzer surveys, whose morphologies are typical of circumstellar shells produced by massive evolved stars. Through spectral similarity with known Luminous Blue Variable (LBV) and Wolf-Rayet (WR) stars, a large population of candidate LBVs (cLBVs) and a smaller number of new WR stars are being discovered. This significantly increases the Galactic cLBV population and confirms that nebulae are inherent to most (if not all) objects of…
On the spatial distribution of luminous blue variables in the M33 galaxy
Special Astrophysical Observatory（特别天文台）；Space Research Institute, Russian Academy of Sciences（俄罗斯科学院空间研究所）；Department of Informatics, University of Zürich（苏黎世大学信息学系）
Context: Star forming early-type galaxies with blue optical colours at low redshift can be used to test our current understanding of galaxy formation and evolution. Aims: We want to reveal the fuel and triggering mechanism for star formation in these otherwise passively evolving red and dead stellar systems. Methods: We undertook an optical and ultraviolet study of 55 star forming blue early-type galaxies, searching for signatures of recent interactions that could be driving the molecular gas into the galaxy and potentially triggering the star formation. Results: We report here our results on …
While bright, blue, compact galaxies are common at $\rm z \sim 1$, they are relatively rare in the local universe, and their evolutionary paths are uncertain. We have obtained resolved H I observations of nine $\rm z \sim 0$ luminous compact blue galaxies (LCBGs) using the Giant Metrewave Radio Telescope and Very Large Array in order to measure their kinematic and dynamical properties and better constrain their evolutionary possibilities. We find that the LCBGs in our sample are rotating galaxies that tend to have nearby companions, relatively high central velocity dispersions, and can have di…
Star-forming blue early-type galaxies at low redshift can give insight to the stellar mass growth of L$*$ elliptical galaxies in the local Universe. We wish to understand the reason for star formation in these otherwise passively evolving red and dead stellar systems. The fuel for star formation can be acquired through recent accretion events such as mergers or flyby. The signatures of such events should be evident from a structural analysis of the galaxy image. We carried out structural analysis on SDSS $r$-band imaging data of 55 star-forming blue elliptical galaxies, derived the structural …
Using deep Hubble and Spitzer observations Oesch et al. (2016) have identified a bright ($M_{\rm UV}\approx -22$) star forming galaxy candidate at $z \approx 11$. The presence of GN-$z11$ implies a number density $\sim 10^{-6}\,{\rm Mpc^{-3}}$, roughly an order of magnitude higher than the expected value based on extrapolations from lower redshift. Using the unprecedented volume and high resolution of the BlueTides cosmological hydrodynamical simulation, we study the population of luminous rare objects at $z > 10$. The luminosity function in BlueTides implies an enhanced number of massive gala…
We report molecular line and dust continuum observations, made with the SEST telescope, towards four young high-mass star forming regions associated with highly luminous (L> 6x10^5 Lsun) IRAS sources (15290-5546, 15502-5302, 15567-5236 and 16060-5146). Molecular emission was mapped in lines of CS (J=2-1, 3-2 and 5-4), SiO (J=2-1 and 3-2), CH3OH (Jk=3k-2k and 2k-1k), and C34S (J=3-2). In addition, single spectra at the peak position were taken in the CO, 13CO and C18O (J=1-0) lines. We find that the luminous star forming regions are associated with molecular gas and dust structures with radii o…
We have studied the spectral time variations of candidate luminous blue variable stars (cLBV) in two low-metallicity blue compact dwarf galaxies, DDO 68 and PHL 293B. The LBV in DDO 68, located in HII region #3, shows an outburst, with an increase of more than 1000 times in Halpha luminosity during the period 2008-2010. The broad emission of the HI and HeI lines display a P Cygni profile, with a relatively constant terminal velocity of ~800 km/s, reaching a maximum luminosity L(Halpha) of ~2x10^38 erg/s, with a FWHM of ~1000-1200 km/s. On the other hand, since the discovery of a cLBV in 2001 i…
(abridged) We present the X-ray analysis of a sample of 30 luminous quasars at $z\simeq3.0-3.3$ with deep XMM-Newton observations, selected from the SDSS-DR7 to be representative of the most luminous, intrinsically blue quasar population. By construction, the sample boasts a unique degree of homogeneity in terms of optical/UV properties. In the X-rays, only four sources are too faint for a detailed spectral analysis. Neglecting a radio-loud object, the other 25 quasars are, as a whole, the most X-ray luminous ever observed, with rest-frame 2-10 keV luminosities of $0.5-7\times10^{45}$ erg/s. T…
We report on the discovery of a luminous blue variable (LBV) lying ~7 pc in projection from the Quintuplet cluster. This source, which we call LBV G0.120-0.048, was selected for spectroscopy owing to its detection as a strong source of Paschen-alpha excess in a recent narrowband imaging survey of the Galactic center region with HST/NICMOS. The K-band spectrum is similar to that of the Pistol Star and other known LBVs. The new LBV was previously cataloged as a photometric variable star, exhibiting brightness fluctuations of up to ~1 mag between 1994 and 1997, with significant variability also o…
Despite advances in observational data, theoretical models, and computational techniques to simulate key physical processes in the formation and evolution of galaxies, the stellar mass assembly of galaxies still remains an unsolved problem today. Optical spectroscopic measurements appear to show that the gas-phase metallicities of local ultra-luminous infrared galaxies (ULIRGs) are significantly lower than those of normal star-forming galaxies. This difference has resulted in the claim that ULIRGs are fueled by metal-poor gas accretion from the outskirts\cite{Mannucci10}. Here we report on a n…
G79.29+0.46 is a nebula created by a Luminous Blue Variable (LBV) star candidate characterized by two almost circular concentric shells. In order to investigate whether the shells are interacting with the infrared dark cloud (IRDC) G79.3+0.3 located at the southwestern border of the inner shell, we conducted Jansky Very Large Array observations of NH3(1,1), (2,2) and c-C3H2, and combined them with previous Effelsberg data. The overall NH3 emission consists of one main clump, named G79A, elongated following the shape of the IRDC, plus two fainter and smaller cores to the north, which spatially …
We identify IRAS 16115-5044, which was previously classified as a protoplanetary nebula (PPN), as a candidate luminous blue variable (LBV). The star has high luminosity (>10$^{5.75}$ L_Sun), ensuring supergiant status, has a temperature similar to LBVs, is photometrically and spectroscopically variable, and is surrounded by warm dust. Its near-infrared spectrum shows the presence of several lines of HI, He I, Fe II, Fe [II], MgII, and Na I with shapes ranging from pure absorption and P Cygni profiles to full emission. These characteristics are often observed together in the relatively rare LBV…
We report the discovery of BOSS-EUVLG1 at z=2.469, by far the most luminous, almost un-obscured star-forming galaxy known at any redshift. First classified as a QSO within the Baryon Oscillation Spectroscopic Survey, follow-up observations with the Gran Telescopio Canarias reveal that its large luminosity, MUV = -24.40 and log(L_Lya/erg s-1) = 44.0, is due to an intense burst of star-formation, and not to an AGN or gravitational lensing. BOSS-EUVLG1 is a compact (reff = 1.2 kpc), young (4-5 Myr) starburst with a stellar mass log(M*/Msun) = 10.0 +/- 0.1 and a prodigious star formation rate of ~…
We investigated the properties of AGN environments, particularly environments where the association of luminous galaxies (LGs) is found within 4~Mpc from AGNs with redshifts of 0.8 -- 1.1. For comparison, three additional AGN environments, (namely, AGNs of all types, type~1 AGNs with X-ray and/or radio detection, and type~2 AGNs) and an environment of blue $M_{*}$, characteristic luminosity of the Schechter function, galaxies were investigated. The cross-correlation function with the surrounding galaxies was measured and compared between the AGN and blue galaxy samples. We also compared the di…
We present 1.3- and/or 3-mm continuum images and 3-mm spectral scans, obtained using NOEMA and ALMA, of 21 distant, dusty, star-forming galaxies (DSFGs). Our sample is a subset of the galaxies selected by Ivison et al. (2016) on the basis of their extremely red far-infrared (far-IR) colours and low {\it Herschel} flux densities; most are thus expected to be unlensed, extraordinarily luminous starbursts at $z \gtrsim 4$, modulo the considerable cross-section to gravitational lensing implied by their redshift. We observed 17 of these galaxies with NOEMA and four with ALMA, scanning through the 3…
We use the combined photometric SDSS + GALEX database to look for populations of luminous blue star-forming galaxies. These were initially identified from such a sample at redshifts near 0.4, using SDSS spectra. We make use of the colour index previously defined to separate stars and QSOs, to locate more of these unusual galaxies, to fainter limits. They are found in significant numbers in two different regions of the related colour-magnitude plot. Within these regions, we use the ensemble 7-colour photometry to estimate the populations of blue star-forming galaxies at redshift near 0.4, and a…
We evaluate the place of Eta Carinae amongst the class of luminous blue variables (LBVs) and show that the LBV phenomenon is not restricted to extremely luminous objects like Eta Car, but extends luminosities as low as log(L/Lsun) = 5.4 - corresponding to initial masses ~25 Msun, and final masses as low as ~10-15 Msun. We present a census of S Doradus variability, and discuss basic LBV properties, their mass-loss behaviour, and whether at maximum light they form pseudo-photospheres. We argue that those objects that exhibit giant Eta Car-type eruptions are most likely related to the more common…
We study H-alpha, far- and near-ultraviolet luminosity functions (LF) of the sample of 795 luminous compact star-forming galaxies with z<0.65. The parameters of optimal functions for LFs are obtained using the maximum likelihood method and the accuracy of fitting is estimated with the chi-squared method. We find that these LFs cannot be reproduced by the Schechter function because of an excess of very luminous galaxies. On the other hand, the Saunders function, the log-normal distribution and some new related functions are good approximations of LFs. The fact that LFs are not reproduced by the…
We construct a sample of 10,680 wall galaxies and 3,064 void galaxies with $M_R \lesssim -20$ by cross referencing a void catalog from literature with Baryon Oscillation Spectroscopic Survey (BOSS) CMASS and WiggleZ galaxies, where the CMASS survey targets redder galaxies and the WiggleZ survey targets bluer galaxies. Comparing the density profiles of the red and blue galaxies as a function of the void radius, we find that the number ratio of red-to-blue galaxies increases with distances from the void centers, suggesting a deficit of luminous and normal red galaxies in voids. We find a mean (g…
We look at the contribution of different galaxy populations to the atomic hydrogen (HI) mass function (HIMF) and the HI density parameter, $Ω_{\text{HI}}$, in the local Universe. Our analysis is based on a sample of 7857 HI-selected galaxies selected from a volume common to the SDSS and ALFALFA surveys (40$\%$ catalog -- $α.40$). We define different populations of galaxies in the color(u-r)-magnitude($M_{\text{r}}$) plane and compute the HIMF for each of them. Additionally we compute the HIMF for dark galaxies; these are undetected in SDSS and represent $\sim 2\%$ of the total sample. We find …
Lyman break analogues (LBAs) are a population of star-forming galaxies at low redshift (z ~ 0.2) selected in the ultraviolet (UV). These objects present higher star formation rates and lower dust extinction than other galaxies with similar masses and luminosities in the local universe. In this work we present results from a survey with the Combined Array for Research in Millimetre-wave Astronomy (CARMA) to detect CO(1-0) emission in LBAs, in order to analyse the properties of the molecular gas in these galaxies. Our results show that LBAs follow the same Schmidt-Kennicutt law as local galaxies…
The hot massive luminous blue variables (LBVs) represent an important evolutionary phase of massive stars. Here, we report the discovery of a new LBV -- LAMOST J0037+4016 in the distant outskirt of the Andromeda galaxy. It is located in the south-western corner (a possible faint spiral arm) of M31 with an unexpectedly large projection distance of $\sim$ 22 kpc from the center. The optical light curve shows a 1.2 mag variation in $V$ band and its outburst and quiescence phases both last over several years. The observed spectra indicate an A-type supergiant at epoch close to the outburst phase a…
We use new near-infrared spectroscopic observations to investigate the nature and evolution of the most luminous Hα(Ha) emitters at z~0.8-2.23, which evolve strongly in number density over this period, and compare them to more typical Ha emitters. We study 59 luminous Ha emitters with $L_{Hα}>L_{Hα}^*$, roughly equally split per redshift slice at z~0.8, 1.47 and 2.23 from the HiZELS and CF-HiZELS surveys. We find that, overall, 30$\pm$8% are AGN (80$\pm$30% of these AGN are broad-line AGN, BL-AGN), and we find little to no evolution in the AGN fraction with redshift, within the errors. However…
Stars more massive than about 8 Msun end their lives as a Supernova (SN), an event of fundamental importance Universe-wide. Theoretically, these stars have been expected to be either at the red supergiant, blue supergiant, or Wolf-Rayet stage before the explosion. We performed coupled stellar evolution and atmospheric modeling of stars with initial masses between 20 Msun and 120 Msun. We found that the 20 Msun and 25 Msun rotating models, before exploding as SN, have spectra that do not resemble any of the aforementioned classes of massive stars. Rather, they have remarkable similarities with …
Luminous Blue Variables (LBVs) are massive stars that show strong spectral and photometric variability. The question of what evolutionary stages they represent and what exactly drives their instability is still open, and thus is it important to understand whether LBVs without significant ongoing activity exist, and for how long such dormant LBVs may ``sleep''. In this article we investigate the long-term variability properties of the LBV candidate MN112, by combining its optical and infrared spectral data covering 12 years with photometric data covering nearly a century acquired by both modern…
We present sensitive NIR (J, H and K) imaging observations toward four luminous massive star forming regions in the Norma Spiral Arm: G324.201+0.119, G328.307+0.432, G329.337+0.147 and G330.949-0.174. We identify three clusters of young stellar objects (YSO) based on surface density diagnostics. We also find that sources detected only in the H and K-bands and with colors corresponding to spectral types earlier than B2, are likely YSOs. We analyze the spatial distribution of stars of different masses and find signatures in two clusters of primordial mass segregation which can't be explained as …
We present a multi-wavelength study of the Galactic Luminous Blue Variable HR Carinae, based on new high resolution mid-infrared (IR) and radio images obtained with the Very Large Telescope (VLT) and the Australia Telescope Compact Array (ATCA), which have been complemented by far-infrared Herschel-PACS observations and ATCA archive data. The Herschel images reveal the large-scale distribution of the dusty emitting nebula, which extends mainly to the North-East direction, up to 70 arcsec from the central star, and is oriented along the direction of the space motion of the star. In the mid-infr…
In the standard view of massive star evolution, luminous blue variables (LBVs) are transitional objects between the most massive O-type stars and Wolf-Rayet (WR) stars. With short lifetimes, these stars should all be found near one another. A recent study of LBVs in the Large Magellanic Cloud (LMC) found instead that LBVs are considerably more isolated than either O-type stars or WRs, with a distribution intermediate between that of the WRs and red supergiants (RSGs). A similar study, using a more restricted sample of LBVs, reached the opposite conclusion. Both studies relied upon the distance…
We present multi-epoch, multi-colour pre-outburst photometry and post-outburst light curves and spectra of the luminous blue variable (LBV) outburst Gaia16cfr discovered by the Gaia satellite on 1 December 2016. We detect Gaia16cfr in 13 epochs of Hubble Space Telescope imaging spanning phases of 10 yr to 8 months before the outburst and in Spitzer Space Telescope imaging 13 years before outburst. Pre-outburst optical photometry is consistent with an 18 Msun F8 I star, although the star was likely reddened and closer to 30 Msun. The pre-outburst source exhibited a significant near-infrared exc…
We report the detection of the most luminous high-redshift Lyman Alpha Emitting galaxy (LAE) yet seen, with log L(Ly alpha) = 43.9 ergs/s. The galaxy -- COSMOS Lyman alpha 1, or COLA1 -- was detected in a search for ultra-luminous LAEs with Hyper Suprime-Cam on the Subaru telescope. It was confirmed to lie at z = 6.593 based on a Lyman alpha line detection obtained from followup spectroscopy with the DEIMOS spectrograph on Keck2. COLA1 is the first very high-redshift LAE to show a multi-component Lyman alpha line profile with a blue wing, which suggests that it could lie in a highly ionized re…
We have found three new LBV candidates in the star-forming galaxy NGC 4736. They show typical well-known LBV spectra, broad and strong hydrogen lines, He I lines, many Fe II lines, and forbidden [Fe II] and [Fe III]. Using archival Hubble Space Telescope and ground-based telescope data, we have estimated the bolometric magnitudes of these objects from -8.4 to -11.5, temperatures, and reddening. Source NGC 4736_1 (Mv = -10.2 +/- 0.1 mag) demonstrated variability between 2005 and 2018 as Delta V = 1.1 mag and Delta B = 0.82 mag, the object belongs to LBV stars. NGC 4736_2 (Mv < -8.6 mag) shows P…
We predict quantitative mass-loss rates and terminal wind velocities for early-type supergiants and luminous blue variables (LBVs) using a dynamical version of the Monte Carlo radiative transfer method. First, the observed drop in terminal wind velocity around spectral type B1 is confirmed by the Monte Carlo method -- at the correct effective temperature of about 21 000 K. This drop in wind velocity is much steeper than would be expected from the drop in escape speed for cooler stars. The results may be particularly relevant for slow winds inferred for some High-Mass X-ray binaries. Second, th…
We study the kinematics of luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC). Using high-resolution spectra, we measure the systemic radial velocities for a sample of 16 LBVs and LBV candidates. In order to measure the net motion of LBVs compared to their local environments, we subtract the projected line-of-sight velocity at the same location derived from the rotation curve model of the LMC. Using nebular and wind emission lines, we infer a velocity dispersion for LBVs of $40.0^{+9.9}_{-6.6}$ km s$^{-1}$. To put LBVs in context with other evolved massive stars, we compare thi…
