Ongoing Star Formation Research Articles

The straight and isolated G350.54+0.69 filament: density profile and star formation content

We investigate the global properties of the straight and isolated filamentary cloud G350.54+0.69 using Herschel continuum and APEX molecular line data. The overall straight morphology is similar to two other well studied nearby filaments (Musca and Taurus-B211/3) while the isolated nature of G350.54+0.69 appears similar to Musca. G350.54+0.69 is composed of two distinct filaments with a length ~5.9 pc for G350.5-N (~2.3 pc for G350.5-S), a total mass of ~810 $M_{\odot}$ (~ 110 $M_{\odot}$), and a mean temperature of ~ 18.2 K (~17.7 K). We identify 9 dense and gravitationally bound cores in the whole cloud G350.54+0.69. The separations between cores and the line mass of the whole cloud appear to follow the predictions of the "sausage" instability theory, which suggests that G350.54+0.69 could have undergone radial collapse and fragmentation. The presence of young protostars is consistent with this hypothesis. The line masses of the two filaments (~120 $M_{\odot}$ pc$^{-1}$ for G350.5-N, and ~45 $M_{\odot}$ pc$^{-1}$ for G350.5-S), mass-size distributions of the dense cores, and low-mass protostars collectively suggest that G350.54+0.69 is a site of ongoing low-mass star formation. Based on the above evidence, we place G350.54+0.69 in an intermediate evolutionary state between Musca and Taurus-B211/3. We suggest that investigations into straight (and isolated) versus those distributed inside molecular clouds may provide important clues into filament formation and evolution.

UVIT view of ram-pressure stripping in action: star formation in the stripped gas of the GASP jellyfish galaxy JO201 in Abell 85

Jellyfish are cluster galaxies that experience strong ram-pressure effects that strip their gas. Their H$\alpha$ images reveal ionized gas tails up to 100 kpc, which could be hosting ongoing star formation. Here we report the ultraviolet (UV) imaging observation of the jellyfish galaxy JO201 obtained at a spatial resolution $\sim$ 1.3 kpc. The intense burst of star formation happening in the tentacles is the focus of the present study. JO201 is the "UV-brightest cluster galaxy" in Abell 85 ($z \sim$ 0.056) with knots and streams of star formation in the ultraviolet. We identify star forming knots both in the stripped gas and in the galaxy disk and compare the UV features with the ones traced by H$\alpha$ emission. Overall, the two emissions remarkably correlate, both in the main body and along the tentacles. Similarly, also the star formation rates of individual knots derived from the extinction-corrected FUV emission agree with those derived from the H$\alpha$ emission and range from $\sim$ 0.01 -to- 2.07 $M_{\odot} \, yr^{-1}$. The integrated star formation rate from FUV flux is $\sim$ 15 $M_{\odot} \, yr^{-1}$. The unprecedented deep UV imaging study of the jellyfish galaxy JO201 shows clear signs of extraplanar star-formation activity due to a recent/ongoing gas stripping event.

History and destiny of an emerging early-type galaxy

Context. The merging of galaxies is one key aspect in our favourite hierarchical ΛCDM Universe and is an important channel leading to massive quiescent elliptical galaxies. Understanding this complex transformational process is ongoing. Aims. We aim to study NGC 7252, which is one of the nearest major-merger galaxy remnants, observed ~1 Gyr after the collision of presumably two gas-rich disc galaxies. It is therefore an ideal laboratory to study the processes inherent to the transformation of disc galaxies to ellipticals. Methods. We obtained wide-field IFU spectroscopy with the VLT-VIMOS integral-field spectrograph covering the central 50′′ × 50′′ of NGC 7252 to map the stellar and ionised gas kinematics, and the distribution and conditions of the ionised gas, revealing the extent of ongoing star formation and recent star formation history. Results. Contrary to previous studies, we find the inner gas disc not to be counter-rotating with respect to the stars. In addition, the stellar kinematics appear complex with a clear indication of a prolate-like rotation component which suggests a polar merger configuration. The ongoing star formation rate is 2.2 ± 0.6 M⊙ yr−1 and implies a typical depletion time of ~2 Gyr given the molecular gas content. Furthermore, the spatially resolved star formation history suggests a slight radial dependence, moving outwards at later times. We confirm a large AGN-ionised gas cloud previously discovered ~5 kpc south of the nucleus, and find a higher ionisation state of the ionised gas at the galaxy centre relative to the surrounding gas disc. Although the higher ionisation towards the centre is potentially degenerate within the central star forming ring, it may be associated with a low-luminosity AGN. Conclusions. Although NGC 7252 has been classified as post-starburst galaxy at the centre, the elliptical-like major-merger remnant still appears very active. A central kpc-scale gas disc has presumably re-formed quickly within the last 100 Myr after final coalescence. The disc features ongoing star formation, implying Gyr long timescale to reach the red sequence through gas consumption alone. While NGC 7252 is useful to probe the transformation from discs to ellipticals, it is not well-suited to study the transformation from blue to red at this point.

Dissecting star formation in the “Atoms-for-Peace” galaxy

Context. The tidal tails of post-merger galaxies exhibit ongoing star formation far from their disks. The study of such systems can be useful for our understanding of gas condensation in diverse environments. Aims. The ongoing star formation in the tidal tails of post-merger galaxies can be directly studied from ultraviolet (UV) imaging observations. Methods. The post merger galaxy NGC7252 (“Atoms-for-Peace” galaxy) is observed with the Astrosat UV imaging telescope (UVIT) in broadband NUV and FUV filters to isolate the star-forming regions in the tidal tails and study the spatial variation in star formation rates. Results. Based on ultraviolet imaging observations, we discuss star-forming regions of ages <200 Myr in the tidal tails. We measure star formation rates in these regions and in the main body of the galaxy. The integrated star formation rate (SFR) of NGC7252 (i.e., that in the galaxy and tidal tails combined) without correcting for extinction is found to be 0.81 ± 0.01 M⊙ yr−1. We show that the integrated SFR can change by an order of magnitude if the extinction correction used in SFR derived from other proxies are taken into consideration. The star formation rates in the associated tidal dwarf galaxies (NGC7252E, SFR = 0.02 M⊙ yr−1 and NGC7252NW, SFR = 0.03 M⊙ yr−1) are typical of dwarf galaxies in the local Universe. The spatial resolution of the UV images reveals a gradient in star formation within the tidal dwarf galaxy. The star formation rates show a dependence on the distance from the centre of the galaxy. This can be due to the different initial conditions responsible for the triggering of star formation in the gas reservoir that was expelled during the recent merger in NGC7252.

Star formation complexes in the ‘galaxy-sized’ supergiant shell of the galaxy HolmbergI

We present the results of observations of the galaxy Holmberg I carried out at the Russian 6-m telescope in the narrow-band imaging, long-slit spectroscopy, and scanning Fabry-Perot interferometer modes. A detailed analysis of gas kinematics, ionization conditions, and metallicity of star-forming regions in the galaxy is presented. The aim of the paper is to analyse the propagation of star formation in the galaxy and to understand the role of the ongoing star formation in the evolution of the central 'galaxy-sized' supergiant HI shell (SGS), where all regions of star formation are observed. We show that star formation in the galaxy occurs in large unified complexes rather than in individual giant HII regions. Evidence of the triggered star formation is observed both on scales of individual complexes and of the whole galaxy. We identified two supernova-remnant candidates and one late-type WN star and analysed their spectrum and surrounding-gas kinematics. We provide arguments indicating that the SGS in Holmberg I is destructing by the influence of star formation occurring on its rims.

Illuminating Low Surface Brightness Galaxies with the Hyper Suprime-Cam Survey

Abstract We present a catalog of extended low surface brightness galaxies (LSBGs) identified in the Wide layer of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first ∼200 deg2 of the survey, we have uncovered 781 LSBGs, spanning red (g − i ≥ 0.64) and blue (g − i < 0.64) colors and a wide range of morphologies. Since we focus on extended galaxies (r eff = 2.″5–14″), our sample is likely dominated by low-redshift objects. We define LSBGs to have mean surface brightnesses mag arcsec−2, which allows nucleated galaxies into our sample. As a result, the central surface brightness distribution spans a wide range of μ 0(g) = 18–27.4 mag arcsec−2, with 50% and 95% of galaxies fainter than 24.3 and 22 mag arcsec−2, respectively. Furthermore, the surface brightness distribution is a strong function of color, with the red distribution being much broader and generally fainter than that of the blue LSBGs, and this trend shows a clear correlation with galaxy morphology. Red LSBGs typically have smooth light profiles that are well characterized by single-component Sérsic functions. In contrast, blue LSBGs tend to have irregular morphologies and show evidence for ongoing star formation. We cross-match our sample with existing optical, H i, and ultraviolet catalogs to gain insight into the physical nature of the LSBGs. We find that our sample is diverse, ranging from dwarf spheroidals and ultradiffuse galaxies in nearby groups to gas-rich irregulars to giant LSB spirals, demonstrating the potential of the HSC-SSP to provide a truly unprecedented view of the LSBG population.

Dynamical evolution of stars and gas of young embedded stellar sub-clusters

We present simulations of the dynamical evolution of young embedded star clusters. Our initial conditions are directly derived from X-ray, infrared, and radio observations of local systems, and our models evolve both gas and stars simultaneously. Our regions begin with both clustered and extended distributions of stars, and a gas distribution which can include a filamentary structure in addition to gas surrounding the stellar subclusters. We find that the regions become spherical, monolithic, and smooth quite quickly, and that the dynamical evolution is dominated by the gravitational interactions between the stars. In the absence of stellar feedback, the gas moves gently out of the centre of our regions but does not have a significant impact on the motions of the stars at the earliest stages of cluster formation. Our models at later times are consistent with observations of similar regions in the local neighbourhood. We conclude that the evolution of young proto-star clusters is relatively insensitive to reasonable choices of initial conditions. Models with more realism, such as an initial population of binary and multiple stars and ongoing star formation, are the next step needed to confirm these findings.

Red Misfits in the Sloan Digital Sky Survey: properties of star-forming red galaxies

We study Red Misfits, a population of red, star-forming galaxies in the local Universe. We classify galaxies based on inclination-corrected optical colours and specific star formation rates derived from the Sloan Digital Sky Survey Data Release 7. Although the majority of blue galaxies are star-forming and most red galaxies exhibit little to no ongoing star formation, a small but significant population of galaxies ($\sim$11 per cent at all stellar masses) are classified as red in colour yet actively star-forming. We explore a number of properties of these galaxies and demonstrate that Red Misfits are not simply dusty or highly-inclined blue cloud galaxies or quiescent red galaxies with poorly-constrained star formation. The proportion of Red Misfits is nearly independent of environment and this population exhibits both intermediate morphologies and an enhanced likelihood of hosting an AGN. We conclude that Red Misfits are a transition population, gradually quenching on their way to the red sequence and this quenching is dominated by internal processes rather than environmentally-driven processes. We discuss the connection between Red Misfits and other transition galaxy populations, namely S0's, red spirals and green valley galaxies.

Exploring the dust content of galactic winds with Herschel – II. Nearby dwarf galaxies

We present the results from an analysis of deep Herschel Space Observatory observations of six nearby dwarf galaxies known to host galactic-scale winds. The superior far-infrared sensitivity and angular resolution of Herschel have allowed detection of cold circumgalactic dust features beyond the stellar components of the host galaxies traced by Spitzer 4.5 $\mu$m images. Comparisons of these cold dust features with ancillary data reveal an imperfect spatial correlation with the ionized gas and warm dust wind components. We find that typically $\sim$10-20\% of the total dust mass in these galaxies resides outside of their stellar disks, but this fraction reaches $\sim$60\% in the case of NGC 1569. This galaxy also has the largest metallicity (O/H) deficit in our sample for its stellar mass. Overall, the small number of objects in our sample precludes drawing strong conclusions on the origin of the circumgalactic dust. We detect no statistically significant trends with star formation properties of the host galaxies, as might be expected if the dust were lifted above the disk by energy inputs from on-going star formation activity. Although a case for dust entrained in a galactic wind is seen in NGC 1569, in all cases, we cannot rule out the possibility that some of the circumgalactic dust might be associated instead with gas accreted or removed from the disk by recent galaxy interaction events, or that it is part of the outer gas-rich portion of the disk that lies below the sensitivity limit of the Spitzer 4.5 $\mu$m data.

Jekyll & Hyde: quiescence and extreme obscuration in a pair of massive galaxies 1.5 Gyr after the Big Bang

We obtained ALMA spectroscopy and deep imaging to investigate the origin of the unexpected sub-millimeter emission toward the most distant quiescent galaxy known to date, ZF-COSMOS-20115 at z = 3.717. We show here that this sub-millimeter emission is produced by another massive (M*~ 1011 M⊙), compact (r1∕2 = 0.67 ± 0.14 kpc) and extremely obscured galaxy (AV ~ 3.5), located only 0.43′′ (3.1 kpc) away from the quiescent galaxy. We dub the quiescent and dusty galaxies Jekyll and Hyde, respectively. No dust emission is detected at the location of the quiescent galaxy, implying SFR < 13 M⊙ yr−1 which is the most stringent upper limit ever obtained for a quiescent galaxy at these redshifts. The two sources are spectroscopically confirmed to lie at the same redshift thanks to the detection of [C II]158 in Hyde (z = 3.709), which provides one the few robust redshifts for a highly-obscured “H-dropout” galaxy (H − [4.5] = 5.1 ± 0.8). The [C II] line shows a clear rotating-disk velocity profile which is blueshifted compared to the Balmer lines of Jekyll by 549 ± 60 km s−1, demonstrating that it is produced by another galaxy. Careful de-blending of the Spitzer imaging confirms the existence of this new massive galaxy, and its non-detection in the Hubble images requires extremely red colors and strong attenuation by dust. Full modeling of the UV-to-far-IR emission of both galaxies shows that Jekyll has fully quenched at least 200Myr prior to observation and still presents a challenge for models, while Hyde only harbors moderate star-formation with SFR ≲ 120 M⊙ yr−1, and is located at least a factor 1.4 below the z ~ 4 main sequence. Hyde could also have stopped forming stars less than 200 Myr before being observed; this interpretation is also suggested by its compactness comparable to that of z ~ 4 quiescent galaxies and its low [C II]/FIR ratio, but significant on-going star-formation cannot be ruled out. Lastly, we find that despite its moderate SFR, Hyde hosts a dense reservoir of gas comparable to that of the most extreme starbursts. This suggests that whatever mechanism has stopped or reduced its star-formation must have done so without expelling the gas outside of the galaxy. Because of their surprisingly similar mass, compactness, environment and star-formation history, we argue that Jekyll and Hyde can be seen as two stages of the same quenching process, and provide a unique laboratory to study this poorly understood phenomenon.

Gravitational instability and star formation in NGC 628

The gas-stars instability criterion for infinitesimally thin disc was applied to the galaxy NGC 628. Instead of using the azimuthally averaged profiles of data the maps of the gas surface densities (THINGS, HERACLES), of the velocity dispersions of stars (VENGA) and gas (THINGS) and of the surface brightness of the galaxy (S$^4$G) were analyzed. All these maps were collected for the same region with a noticeable star formation rate and were superimposed on each other. Using the data on the rotation curve values of $Q_\mathrm{eff}$ were calculated for each pixel in the image. The areas within the contours $Q_\mathrm{eff}<3$ were compared with the ongoing star formation regions ($\Sigma_\mathrm{SFR}> 0.007 \, M_{\odot}$yr$^{-1}$kpc$^{-2}$) and showed a good coincidence between them. The Romeo-Falstad disc instability diagnostics taking into account the thickness of the stellar and gas layers does not change the result. If the one-fluid instability criterion is used, the coincidence is worse. The analysis was carried out for the area $r < $ 0.5$r_{25} $. Leroy et al. (2008) using azimuthally averaged data obtained $Q_\mathrm{eff} \approx 3-4$ for this area of the disc, which makes it stable against non-axisymmetric perturbations and gas dissipation, and does not predict the location of star forming regions. Since in the galaxies the distribution of hydrogen and the regions of star formation is often patchy, the relationship between gravitational instability and star formation should be sought using data maps rather than azimuthally averaged data.

The Embedded Ring-like Feature and Star Formation Activities in G35.673-00.847

Abstract We present a multiwavelength study to probe the star formation (SF) process in the molecular cloud linked with the G35.673-00.847 site (hereafter MCG35.6), which is traced in a velocity range of 53–62 km s−1. Multiwavelength images reveal a semi-ring-like feature (associated with ionized gas emission) and an embedded face-on ring-like feature (without the NVSS 1.4 GHz radio emission, where 1σ ∼ 0.45 mJy beam−1) in MCG35.6. The semi-ring-like feature is originated by the ionizing feedback from a star with spectral type B0.5V–B0V. The central region of the ring-like feature does not contain detectable ionized gas emission, indicating that the ring-like feature is unlikely to be produced by the ionizing feedback from a massive star. Several embedded Herschel clumps and young stellar objects (YSOs) are identified in MCG35.6, tracing the ongoing SF activities within the cloud. The polarization information from the Planck and GPIPS data trace the plane-of-sky magnetic field, which is oriented parallel to the major axis of the ring-like feature. At least five clumps (having M clump ∼ 740–1420 M ⊙) seem to be distributed in an almost regularly spaced manner along the ring-like feature and contain noticeable YSOs. Based on the analysis of the polarization and molecular line data, three subregions containing the clumps are found to be magnetically supercritical in the ring-like feature. Altogether, the existence of the ring-like feature and the SF activities on its edges can be explained by the magnetic field mediated process as simulated by Li &amp; Nakamura.

SDSS-IV MaNGA: evidence of the importance of AGN feedback in low-mass galaxies

We present new evidence for AGN feedback in a subset of 69 quenched low-mass galaxies (M⋆ ≲ 5 × 109 M⊙, Mr > −19) selected from the first 2 yr of the Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at APO (SDSS-IV MaNGA) survey. The majority (85 per cent) of these quenched galaxies appear to reside in a group environment. We find six galaxies in our sample that appear to have an active AGN that is preventing on-going star formation; this is the first time such a feedback mechanism has been observed in this mass range. Interestingly, five of these six galaxies have an ionized gas component that is kinematically offset from their stellar component, suggesting the gas is either recently accreted or outflowing. We hypothesize these six galaxies are low-mass equivalents to the ‘red geysers’ observed in more massive galaxies. Of the other 63 galaxies in the sample, we find 8 do appear for have some low level, residual star formation, or emission from hot, evolved stars. The remaining galaxies in our sample have no detectable ionized gas emission throughout their structures, consistent with them being quenched. This work shows the potential for understanding the detailed physical properties of dwarf galaxies through spatially resolved spectroscopy.

“Red” but Not “Dead”: Actively Star-forming Brightest Cluster Galaxies at Low Redshifts

Abstract Brightest cluster galaxies (BCGs) are believed to have assembled most of their stars early in time and therefore should be passively evolving at low redshifts and appear “red-and-dead.” However, there have been reports that a minority of low-redshift BCGs still have ongoing star formation rates (SFRs) of a few to even . Such BCGs are found in “cool-core” (“CC”) clusters, and their star formation is thought to be fueled by “cooling flow.” To further investigate the implications of low-redshift, star-forming BCGs, we perform a systematic search using the 22 μm data (“W4” band) from the Wide-field Infrared Survey Explorer (WISE) on the GMBCG catalog, which contains 55,424 BCGs at identified in the Sloan Digital Sky Survey (SDSS). Our sample consists of 389 BCGs that are bright in W4 (“W4BCGs”), most being brighter than 5 mJy. While some ( ) might host active galactic nuclei, most W4BCGs should owe their strong mid-IR emissions to dust-enshrouded star formation. Their median total IR luminosity (L IR) is (SFR ∼50 , and 27% of the whole sample has (SFR &gt;100 ). Using 10 W4BCGs that have Chandra X-ray data, we show that 7 of them are possibly in CC clusters. However, in most cases (five out of seven) the mass deposition rate cannot account for the observed SFR. This casts doubt on the idea that cooling flows are the cause of the star formation in non-quiescent BCGs.

The Enigmatic (Almost) Dark Galaxy Coma P: The Atomic Interstellar Medium

Abstract We present new high-resolution H i spectral line imaging of Coma P, the brightest H i source in the system HI 1232+20. This galaxy with extremely low surface brightness was first identified in the ALFALFA survey as an “(Almost) Dark” object: a clearly extragalactic H i source with no obvious optical counterpart in existing optical survey data (although faint ultraviolet emission was detected in archival GALEX imaging). Using a combination of data from the Westerbork Synthesis Radio Telescope and the Karl G. Jansky Very Large Array, we investigate the H i morphology and kinematics at a variety of physical scales. The H i morphology is irregular, reaching only moderate maxima in mass surface density (peak pc−2). Gas of lower surface brightness extends to large radial distances, with the H i diameter measured at 4.0 ± 0.2 kpc inside the pc−2 level. We quantify the relationships between mass surface density of H i gas and star formation on timescales of ∼100–200 Myr as traced by GALEX far-ultraviolet emission. While Coma P has regions of dense H i gas reaching the cm−2 level typically associated with ongoing star formation, it lacks massive star formation as traced by Hα emission. The H i kinematics are extremely complex: a simple model of a rotating disk cannot describe the H i gas in Coma P. Using spatially resolved position–velocity analysis we identify two nearly perpendicular axes of projected rotation that we interpret as either the collision of two H i disks or a significant infall event. Similarly, three-dimensional modeling of the H i dynamics provides a best fit with two H i components. Coma P is just consistent (within 3σ) with the known scaling relation. It is either too large for its H i mass, has too low an H i mass for its H i size, or the two H i components artificially extend its H i size. Coma P lies within the empirical scatter at the faint end of the baryonic Tully–Fisher relation, although the complexity of the H i dynamics complicates the interpretation. Along with its large ratio of H i to stellar mass, the collective H i characteristics of Coma P make it unusual among known galaxies in the nearby universe.

Wide-field Imaging of the Environments of LITTLE THINGS Dwarf Irregular Galaxies

Abstract We have obtained wide-field images of 36 of the 41 LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey) nearby (&lt;10.3 Mpc) dwarf irregular and blue compact dwarf galaxies. Although the LITTLE THINGS galaxies were chosen to be non-interacting and no companions were found in H i imaging, the purpose of this imaging was to search for optical companion galaxies that had been missed in imaging with smaller fields of view and that might indicate an external factor in ongoing star formation. The limiting magnitudes of the images range from 19.7 to 28.3 mag arcsec−2, with a median value of 25.9 mag arcsec−2. We did not find any unknown companions. Two of the LITTLE THINGS galaxies, NGC 4163 and NGC 4214, and the fainter dwarf, UGCA 276, lie potentially within 100 kpc of each other, but our imaging does not reveal any stellar bridge between the galaxies. This project was part of the Lowell Amateur Research Initiative.

The stellar mass, star formation rate and dark matter halo properties of LAEs at z ∼ 2

Abstract We present average stellar population properties and dark matter halo masses of z ∼ 2 Lyα emitters (LAEs) from spectral energy distribution fitting and clustering analysis, respectively, using ≃ 1250 objects ($\mathit {NB387}\le 25.5$) in four separate fields of ≃ 1 deg2 in total. With an average stellar mass of 10.2 ± 1.8 × 108 M⊙ and star formation rate of 3.4 ± 0.4 M⊙ yr−1, the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be $4.0_{-2.9}^{+5.1} \times 10^{10}{\,\,}M_{\odot }$ with an effective bias of $1.22^{+0.16}_{-0.18}$, which is lower than that of z ∼ 2 LAEs (1.8 ± 0.3) obtained by a previous study based on a three times smaller survey area, with a probability of 96%. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low H i gas mass, this result appears to be consistent with the observations of a high Lyα escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press–Schechter formalism predicts that at z = 0 our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their star formation rates are largely suppressed after z ∼ 2 as some previous studies have reported for the LMC itself.

The Carnegie Supernova Project I

We aim to improve upon contemporary methods to estimate host-galaxy reddening of stripped-envelope (SE) supernovae (SNe). To this end the Carnegie Supernova Project (CSP-I) SE SN photometry data release, consisting of nearly three dozen objects, is used to identify a minimally reddened sub-sample for each traditionally defined spectroscopic sub-type (i.e., SNe IIb, SNe Ib, SNe Ic). Inspection of the optical and near-infrared (NIR) colors and color evolution of the minimally reddened sub-samples reveals a high degree of homogeneity, particularly between 0 d to +20 d relative to B-band maximum. This motivated the construction of intrinsic color-curve templates, which when compared to the colors of reddened SE SNe, yields an entire suite of optical and NIR color excess measurements. Comparison of optical/optical vs. optical/NIR color excess measurements indicates the majority of the CSP-I SE SNe suffer relatively low amounts of reddening (i.e., E(B−V)host&lt; 0.20 mag) and we find evidence for different RVhost values among different SE SN. Fitting the color excess measurements of the seven most reddened (i.e., E(B−V)host&gt; 0.20 mag) objects with the Fitzpatrick (1999, PASP, 111, 63) reddening law model provides robust estimates of the host visual-extinction AVhost and RVhost. In the case of the SE SNe with relatively low amounts of reddening, a preferred value of RVhost is adopted for each sub-type, resulting in estimates of AVhost through Fitzpatrick (1999) reddening law model fits to the observed color excess measurements. Our analysis suggests SE SNe reside in galaxies characterized by a range of dust properties. We also find evidence that SNe Ic are more likely to occur in regions characterized by larger RVhost values compared to SNe IIb/Ib and they also tend to suffer more extinction. The later finding is consistent with work in the literature suggesting SNe Ic tend to occur in regions of on-going star formation.

Copious Amounts of Dust and Gas in a z = 7.5 Quasar Host Galaxy

Abstract We present IRAM/NOEMA and JVLA observations of the quasar J1342+0928 at z = 7.54 and report detections of copious amounts of dust and [C ii] emission in the interstellar medium (ISM) of its host galaxy. At this redshift, the age of the universe is 690 Myr, about 10% younger than the redshift of the previous quasar record holder. Yet, the ISM of this new quasar host galaxy is significantly enriched by metals, as evidenced by the detection of the [C ii] 158 μm cooling line and the underlying far-infrared (FIR) dust continuum emission. To the first order, the FIR properties of this quasar host are similar to those found at a slightly lower redshift ( ), making this source by far the FIR-brightest galaxy known at . The [C ii] emission is spatially unresolved, with an upper limit on the diameter of 7 kpc. Together with the measured FWHM of the [C ii] line, this yields a dynamical mass of the host of . Using standard assumptions about the dust temperature and emissivity, the NOEMA measurements give a dust mass of . The brightness of the [C ii] luminosity, together with the high dust mass, imply active ongoing star formation in the quasar host. Using [C ii]–SFR scaling relations, we derive star formation rates of 85–545 yr−1 in the host, consistent with the values derived from the dust continuum. Indeed, an episode of such past high star formation is needed to explain the presence of ∼108 M ☉ of dust implied by the observations.

Widespread SiO and CH3OH Emission in Filamentary Infrared-Dark Clouds★

Infrared dark clouds (IRDCs) are cold, dense regions of high (optical and infrared) extinction, believed to be the birthplace of high-mass stars and stellar clusters. The physical mechanisms leading to the formation of these IRDCs are not completely understood and it is thus important to study their molecular gas kinematics and chemical content to search for any signature of the IRDCs formation process. Using the 30-m-diameter antenna at the Instituto de Radioastronomía Milimétrica (IRAM), we have obtained emission maps of dense gas tracers (H13CO+ and HN13C) and typical shock tracers (SiO and CH3OH) towards three IRDCs, G028.37+00.07, G034.43+00.24, and G034.77−00.55 (clouds C, F, and G, respectively). We have studied the molecular gas kinematics in these clouds and, consistent with previous works towards other IRDCs, the clouds show complex gas kinematics with several velocity-coherent substructures separated in velocity space by a few km s−1. Correlated with these complex kinematic structures, widespread (parsec-scale) emission of SiO and CH3OH is present in all the three clouds. For clouds C and F, known to be actively forming stars, widespread SiO and CH3OH is likely associated with on-going star formation activity. However, for cloud G, which lacks either 8 or 24 μm sources and 4.5 μm H2 shock-excited emission, the detected widespread SiO and CH3OH emission may have originated in a large-scale shock interaction, although a scenario involving a population of low-mass stars driving molecular outflows cannot be fully ruled out.