Full Spectral Energy Distribution Research Articles

Absence of nebular He ii λ4686 constrains the UV emission from the Ultraluminous X-ray pulsar NGC 1313 X–2

Abstract While much has been learned in recent decades about the X-ray emission of the extragalactic Ultraluminous X-ray sources (ULXs), their radiative output in the UV band remains poorly constrained. Understanding of the full ULX spectral energy distribution (SED) is imperative to constrain the accretion flow geometry powering them, as well as their radiative power. Here we present constraints on the UV emission of the pulsating ULX (PULX) NGC 1313 X–2 based on the absence of nebular He ii λ4686 emission in its immediate environment. To this end, we first perform multi-band spectroscopy of the ULX to derive three realistic extrapolations of the SED into the unaccessible UV, each predicting varying levels of UV luminosity. We then perform photo-ionization modelling of the bubble nebula and predict the He ii λ4686 fluxes that should have been observed based on each of the derived SEDs. We then compare these predictions with the derived upper limit on He ii λ4686 from MUSE data, which allows us to infer a UV luminosity LUV ≲ 1 × 1039 erg/s in the PULX NGC 1313 X–2. Comparing the UV luminosity inferred with other ULXs, our work suggests there may be an intrinsic difference between hard and soft ULXs, either related to different mass-transfer rates and/or the nature of the accretor. However, a statistical sample of ULXs with inferred UV luminosities is needed to fully determine the distinguishing features between hard and soft ULXs. Finally, we discuss ULXs ionising role in the context of the nebular He ii λ4686 line observed in star-forming, metal-poor galaxies.

Spatial Variations and Breaks in the Optical–Near-infrared Spectra of the Pulsar and Pulsar Wind Nebula in Supernova Remnant 0540–69.3

The supernova remnant (SNR) 0540–69.3, twin of the Crab Nebula, offers an excellent opportunity to study the continuum emission from a young pulsar and pulsar wind nebula (PWN). We present observations taken with the Very Large Telescope instruments MUSE and X-shooter in the wavelength range 3000–25000 Å, which allow us to study spatial variations of the optical spectra, along with the first near-infrared (NIR) spectrum of the source. We model the optical spectra with a power law (PL) F ν ∝ ν −α and find clear spatial variations (including a torus–jet structure) in the spectral index across the PWN. Generally, we find spectral hardening toward the outer parts, from α ∼ 1.1 to ∼0.1, which may indicate particle reacceleration by the PWN shock at the inner edge of the ejecta or alternatively time variability of the pulsar wind. The optical–NIR spectrum of the PWN is best described by a broken PL, confirming that several breaks are needed to model the full spectral energy distribution of the PWN, and suggesting the presence of more than one particle population. Finally, subtracting the PWN contribution from the pulsar spectrum we find that the spectrum is best described with a broken-PL model with a flat and a positive spectral index, in contrast to the Crab pulsar that has a negative spectral index and no break in the optical. This might imply that pulsar differences propagate to the PWN spectra.

ALMA Lensing Cluster Survey: Full Spectral Energy Distribution Analysis of z ∼ 0.5–6 Lensed Galaxies Detected with millimeter Observations

Sub/millimeter galaxies are a key population for the study of galaxy evolution because the majority of star formation at high redshifts occurred in galaxies deeply embedded in dust. To search for this population, we have performed an extensive survey with Atacama Large Millimeter/submillimeter Array (ALMA), called the ALMA Lensing Cluster Survey (ALCS). This survey covers 133 arcmin2 area and securely detects 180 sources at z ∼ 0.5–6 with a flux limit of ∼0.2 mJy at 1.2 mm. Here, we report the results of multiwavelength spectral energy distribution analysis of the whole ALCS sample, utilizing the observed-frame UV to millimeter photometry. We find that the majority of the ALCS sources lie on the star-forming main sequence, with a smaller fraction showing intense starburst activities. The ALCS sample contains high infrared-excess sources ( IRX=log(Ldust/LUV)>1 ), including two extremely dust-obscured galaxies (IRX > 5). We also confirm that the ALCS sample probes a broader range in lower dust mass than conventional submillimeter galaxy samples in the same redshift range. We identify six heavily obscured active galactic nucleus (AGN) candidates that are not detected in the archival Chandra data in addition to the three X-ray AGNs reported by Uematsu et al. (2023). The inferred AGN luminosity density shows a possible excess at z = 2–3 compared with that determined from X-ray surveys below 10 keV.

The recent star formation history of NGC 628 on resolved scales

ABSTRACT Star formation histories (SFHs) are integral to our understanding of galaxy evolution. We can study recent SFHs by comparing the star formation rate (SFR) calculated using different tracers, as each probes a different time-scale. We aim to calibrate a proxy for the present-day rate of change in SFR, dSFR/dt, which does not require full spectral energy distribution (SED) modelling and depends on as few observables as possible, to guarantee its broad applicability. To achieve this, we create a set of models in cigale and define an SFR change diagnostic as the ratio of the SFR averaged over the past 5 and 200 Myr, $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$, probed by the H α–FUV colour. We apply $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ to the nearby spiral NGC 628 and find that its star formation activity has overall been declining in the recent past, with the spiral arms, however, maintaining a higher level of activity. The impact of the spiral arm structure is observed to be stronger on $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ than on the star formation efficiency. In addition, increasing disc pressure tends to increase recent star formation, and consequently $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$. We conclude that $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ is sensitive to the molecular gas content, spiral arm structure, and disc pressure. The $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ indicator is general and can be used to reconstruct the recent SFH of any star-forming galaxy for which H α, FUV, and either mid- or far-IR photometry is available, without the need of detailed modelling.

Spatial disconnection between stellar and dust emissions: The test of the Antennae Galaxies (Arp 244)

Context. The detection of dust-rich high-redshift galaxies with the Atacama Large Millimeter Array (ALMA), the cold dust emission of which is spatially disconnected from the ultraviolet emission, bears a challenge for modelling their spectral energy distributions (SEDs) with codes based on an energy budget between the stellar and dust components. Aims. We want to test the validity of energy balance modelling on a nearby resolved galaxy with vastly different ultraviolet and infrared spatial distributions and to decipher the kinds of information that can be reliably retrieved from the analysis of the full SED. Methods. We used 15 broadband images of the Antennae Galaxies ranging from far-ultraviolet to far-infrared and divided Arp 244 into 58 square ∼1 kpc2 regions. We fit the data with CIGALE to determine the star formation rate, stellar mass, and dust attenuation of each region. We compared these quantities to those obtained for Arp 244 as a whole. Results. The SEDs of the 58 regions and Arp 244 are well fitted. The estimates of the star formation rate and stellar mass for the whole galaxy are found to be consistent – within one sigma – with the same parameters summed over the 58 regions. We present the spatial distribution of these physical parameters as well as the shape of the attenuation curve across the Antennae Galaxies. We find that the Overlap Region exhibits a high star formation rate, attenuation, and a shallow attenuation curve. We observe a flattening of the attenuation curves with increasing attenuation and dust surface density in agreement with the predictions of hydrodynamical simulations coupled with radiative transfer modelling.

Investigating the Accretion Nature of Binary Supermassive Black Hole Candidate SDSS J025214.67−002813.7

Abstract We present results of a multiwavelength analysis of SDSS J025214.67−002813.7, a system that has been previously classified as a binary active galactic nucleus (AGN) candidate based on periodic signals detected in the optical light curves. We use available radio−X-ray observations of the system to investigate the true accretion nature. Analyzing new observations from XMM-Newton and NuSTAR, we characterize the X-ray emission and search for evidence of circumbinary accretion. Although the 0.5–10 keV spectrum shows evidence of an additional soft emission component, possibly due to extended emission from hot nuclear gas, we find the spectral shape is consistent with that of a single AGN. Compiling a full multiwavelength spectral energy distribution (SED), we also search for signs of circumbinary accretion, such as a “notch” in the continuum due to the presence of minidisks. We find that the radio–optical emission agrees with the SED of a standard, radio-quiet, AGN; however, there is a large deficit in emission blueward of ∼1400 Å. Although this deficit in emission can plausibly be attributed to a binary AGN system, we find that the SED of SDSS J0252−0028 is better explained by emission from a reddened, single AGN. However, future studies of the expected hard X-ray emission associated with binary AGNs (especially in the unequal-mass regime) will allow for more rigorous analyses of the binary AGN hypothesis.

First Light And Reionisation Epoch Simulations (FLARES) – III. The properties of massive dusty galaxies at cosmic dawn

ABSTRACT Using the First Light And Reionisation Epoch Simulations (flares), we explore the dust-driven properties of massive high-redshift galaxies at z ∈ [5, 10]. By post-processing, the galaxy sample using the radiative transfer code skirt we obtain the full spectral energy distribution. We explore the resultant luminosity functions, IRX–β relations as well as the luminosity-weighted dust temperatures in the Epoch of Reionisation (EoR). We find that most of our results are in agreement with the current set of observations, but underpredict the number densities of bright IR galaxies, which are extremely biased towards the most overdense regions. We see that the flares IRX–β relation (for 5 ≤ z ≤ 8) pre-dominantly follows the local starburst relation. The IRX shows an increase with stellar mass, plateauing at the high-mass end (∼1010 M⊙) and shows no evolution in the median normalisation with redshift. We also look at the dependence of the peak dust temperature (Tpeak) on various galaxy properties including the stellar mass, IR luminosity, and sSFR, finding the correlation to be strongest with sSFR. The luminosity-weighted dust temperatures increase towards higher redshifts, with the slope of the Tpeak–redshift relation showing a higher slope than the lower redshift relations obtained from previous observational and theoretical works. The results from flares, which are able to provide a better statistical sample of high-redshift galaxies compared to other simulations, provides a distinct vantage point for the high-redshift Universe.

The effect of active galactic nuclei on the cold interstellar medium in distant star-forming galaxies

In the framework of a systematic study with the ALMA interferometer of IR-selected main-sequence and starburst galaxies at z ∼ 1 − 1.7 at typical ∼1″ resolution, we report on the effects of mid-IR- and X-ray-detected active galactic nuclei (AGN) on the reservoirs and excitation of molecular gas in a sample of 55 objects. We find widespread detectable nuclear activity in ∼30% of the sample. The presence of dusty tori influences the IR spectral energy distribution of galaxies, as highlighted by the strong correlation among the AGN contribution to the total IR luminosity budget (fAGN = LIR, AGN/LIR), its hard X-ray emission, and the Rayleigh-Jeans to mid-IR (S1.2 mm/S24 μm) observed color, with evident consequences on the ensuing empirical star formation rate estimates. Nevertheless, we find only marginal effects of the presence and strength of AGN on the carbon monoxide CO (J = 2, 4, 5, 7) or neutral carbon ([C I](3P1 − 3P0), [C I](3P2 − 3P1)) line luminosities and on the derived molecular gas excitation as gauged by line ratios and the full spectral line energy distributions. The [C I] and CO emission up to J = 5, 7 thus primarily traces the properties of the host in typical IR luminous galaxies. However, our analysis highlights the existence of a large variety of line luminosities and ratios despite the homogeneous selection. In particular, we find a sparse group of AGN-dominated sources with the highest LIR, AGN/LIR, SFR ratios, ≳3, that are more luminous in CO (5−4) than what is predicted by the L′CO(5-4)−LIR, SFR relation, which might be the result of the nuclear activity. For the general population, our findings translate into AGN having minimal effects on quantities such as gas and dust fractions and star formation efficiencies. If anything, we find hints of a marginal tendency of AGN hosts to be compact at far-IR wavelengths and to display 1.8 times larger dust optical depths. In general, this is consistent with a marginal impact of the nuclear activity on the gas reservoirs and star formation in average star-forming AGN hosts with LIR > 5 × 1011 L⊙, typically underrepresented in surveys of quasars and submillimeter galaxies.

DirtyGrid II: An Analysis of the Dust and Stellar Properties in Nearby Star-forming Galaxies

Abstract We study the dust and stellar properties of the Spitzer Infrared Nearby Galaxies Survey galaxies by fitting the ultraviolet (UV) to far-infrared (FIR) spectral energy distributions using the DirtyGrid stellar and dust radiative transfer models. We find a minimum of two components of different stellar ages are needed, representing a young and an old stellar population, in order to obtain good fits for most of the galaxies. Our total dust masses agree with literature dust masses to within a factor of 2, and the residuals correlate most strongly with the stellar mass surface density of the old component. The LMC-2 dust grain model best describes the dust found in these normal star-forming galaxies. The derived attenuation curves are steeper than those found previously for starburst galaxies, and possess a weak 2175 Å feature. The relative contribution of the young and old stellar components as a function of wavelength reveals that the young component dominates the far-UV and MIPS24 bands, the old component dominates the optical/near-IR bands, and both components are important for the FIR bands. The DirtyGrid star formation rates (SFRs) are consistent with a number of literature SFR indicators within a factor of 2. The differences we find are primarily due to the influence of the old stellar population that are accounted for by the DirtyGrid SFRs fitting on a galaxy-by-galaxy basis using the information present in the full UV-FIR spectral energy distribution.

Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. I. An Accurate Look at the L-to-T Transition at ∼300 Myr from Optical Through Mid-infrared Spectrophotometry

Abstract We present Spitzer IRS 5–14 μm spectra and 16 μm and 22 μm photometry of the T2.5 companion to the ∼300 Myr old G0V star HN Peg. We incorporate previous 0.8–5 μm observations to obtain the most comprehensive spectral energy distribution (SED) of an intermediate-gravity L/T-transition dwarf that, together with an accurate Gaia EDR3 parallax of the primary, enables us to derive precise fundamental parameters. We find that young (≈0.1–0.3 Gyr) early-T dwarfs on average have ≈140 K lower effective temperatures, ≈20% larger radii, and similar bolometric luminosities compared to ≳1 Gyr old field dwarfs with similar spectral types. Our accurate infrared spectrophotometry offers new detail at wavelengths where the dominant carbon-bearing molecules have their strongest transitions: at 3.4 μm for methane and at 4.6 μm for carbon monoxide. We assess the performance of various widely available photospheric models and find that models with condensates and/or clouds better reproduce the full SED of this moderately young early-T dwarf. However, cloud-free models incorporating a more general convective instability treatment reproduce at least the low-resolution near-infrared spectrum similarly well. Our analysis of R ≈ 2300 J-band spectra shows that the near-infrared potassium absorption lines in HN Peg B have similar strengths to those seen in both younger and older T2–T3 dwarfs. We conclude that while alkali lines are well established as surface gravity indicators for L-type or warmer stars, they are insensitive to surface gravity in early-T dwarfs.

Cold dust and stellar emissions in dust-rich galaxies observed with ALMA: a challenge for SED-fitting techniques

Context. Over the past few years the Atacama Large Millimeter Array (ALMA) has detected dust-rich galaxies whose cold dust emission is spatially disconnected from the ultraviolet (UV) rest-frame emission. This represents a challenge for modeling their spectral energy distributions (SED) with codes based on an energy budget between the stellar and dust components. This could potentially weaken the solidity of the physical parameters measured with these modeling tools. Aims. We want to verify the validity of energy balance modeling on a sample of galaxies observed from the UV to the sub-millimeter rest frame with ALMA and decipher what information can be reliably retrieved from the analysis of the full SED and from subsets of wavelengths. Methods. We select 17 sources at z ≃ 2 in the Hubble Ultra-Deep Field (HUDF) and in the GOODS-South field detected with ALMA and Herschel and for which UV to near-infrared rest-frame ancillary data are available. We fit the data with CIGALE exploring different configurations for dust attenuation and star formation histories, considering either the full dataset or one that is reduced to the stellar and dust emission. We compare estimates of the dust luminosities, star formation rates, and stellar masses. Results. The fit of the stellar continuum alone with the starburst attenuation law can only reproduce up to 50% of the total dust luminosity observed by Herschel and ALMA. This deficit is found to be marginally consistent with similar quantities estimated in the COSMOS field and is found to increase with the specific star formation rate. The combined stellar and dust SEDs are well fitted when different attenuation laws are introduced. Shallow attenuation curves are needed for the galaxies whose cold dust distribution is very compact compared to starlight. The stellar mass estimates are affected by the choice of the attenuation law. The star formation rates are robustly estimated as long as dust luminosities are available. The large majority of the galaxies are above the average main sequence of star forming galaxies and one source is a strong starburst.

Star-forming galaxies at low-redshift in the SHARDS survey

Context. The physical processes driving the evolution of star formation (SF) in galaxies over cosmic time still present many open questions. Recent galaxy surveys allow now to study these processes in great detail at intermediate redshift (0 ≤ z ≤ 0.5). Aims. We build a complete sample of star-forming galaxies and analyze their properties, reaching systems with low stellar masses and low star formation rates (SFRs) at intermediate-to-low redshift. Methods. We use data from the SHARDS multiband survey in the GOODS-North field. Its depth (up to magnitude ⟨m3σ⟩~ 26.5) and its spectro-photometric resolution (R ~ 50) provides us with an ideal dataset to search for emission line galaxies (ELGs). We develop a new algorithm to identify low-redshift (z < 0.36) ELGs by detecting the [OIII]5007 and Hα emission lines simultaneously. We fit the spectral energy distribution (SED) of the selected sample, using a model with two single stellar populations. Results. We find 160 star-forming galaxies for which we derive equivalent widths (EWs) and absolute fluxes of both emission lines. We detect EWs as low as 12 Å, with median values for the sample of ~35 Å in [OIII]5007 and ~56 Å in Hα, respectively. Results from the SED fitting show a young stellar population with low median metallicity (36% of the solar value) and extinction (AV ~ 0.37), with median galaxy stellar mass ~108.5 M⊙. Gas-phase metallicities measured from available spectra are also low. ELGs in our sample present bluer colours in the UVJ plane than the median colour-selected star-forming galaxy in SHARDS. We suggest a new V-J colour criterion to separate ELGs from non-ELGs in blue galaxy samples. In addition, several galaxies present high densities of O-type stars, possibly producing galactic superwinds, which makes them interesting targets for follow-up spectroscopy. Conclusions. We have demonstrated the efficiency of SHARDS in detecting low-mass ELGs (~2 magnitudes deeper than previous spectroscopic surveys in the same field). The selected sample accounts for 20% of the global galaxy population at this redshift and luminosity, and is characterized by young SF bursts with sub-solar metallicities and low extinction. However, robust fits to the full SEDs can only be obtained including an old stellar population, suggesting the young component is built up by a recent burst of SF in an otherwise old galaxy.

Empirical Bolometric Fluxes and Angular Diameters of 1.6 Million Tycho-2 Stars and Radii of 350,000 Stars with Gaia DR1 Parallaxes

Abstract We present bolometric fluxes and angular diameters for over 1.6 million stars in the Tycho-2 catalog, determined using previously determined empirical color-temperature and color-flux relations. We vet these relations via full fits to the full broadband spectral energy distributions for a subset of benchmark stars and perform quality checks against the large set of stars for which spectroscopically determined parameters are available from LAMOST, RAVE, and/or APOGEE. We then estimate radii for the 355,502 Tycho-2 stars in our sample whose Gaia DR1 parallaxes are precise to . For these stars, we achieve effective temperature, bolometric flux, and angular diameter uncertainties of the order of 1%–2% and radius uncertainties of order 8%, and we explore the effect that imposing spectroscopic effective temperature priors has on these uncertainties. These stellar parameters are shown to be reliable for stars with ≲ 7000 K. The over half a million bolometric fluxes and angular diameters presented here will serve as an immediate trove of empirical stellar radii with the Gaia second data release, at which point effective temperature uncertainties will dominate the radius uncertainties. Already, dwarf, subgiant, and giant populations are readily identifiable in our purely empirical luminosity-effective temperature (theoretical) Hertzsprung–Russell diagrams.

A Controlled Study of Cold Dust Content in Galaxies from z = 0–2

Abstract At , the formation of new stars is dominated by dusty galaxies whose far-IR emission indicates they contain colder dust than local galaxies of a similar luminosity. We explore the reasons for the evolving IR emission of similar galaxies over cosmic time using (1) local galaxies from GOALS ( ), (2) galaxies at from 5MUSES ( ), and (3) IR luminous galaxies spanning from GOODS and Spitzer xFLS ( ). All samples have Spitzer mid-IR spectra, and Herschel and ground-based submillimeter imaging covering the full IR spectral energy distribution, allowing us to robustly measure , , and for every galaxy. Despite similar infrared luminosities, dusty star-forming galaxies (DSFG) have a factor of 5 higher dust masses and 5 K colder temperatures. The increase in dust mass is linked to an increase in the gas fractions with redshift, and we do not observe a similar increase in stellar mass or star formation efficiency. , a proxy for , is strongly correlated with independently of redshift. We measure merger classification and galaxy size for a subsample, and there is no obvious correlation between these parameters and or . In DSFG, the change in can fully account for the observed colder dust temperatures, suggesting that any change in the spatial extent of the interstellar medium is a second-order effect.

The full spectral radiative properties of Proxima Centauri

The discovery of Proxima b, a terrestrial temperate planet, presents the opportunity of studying a potentially habitable world in optimal conditions. A key aspect to model its habitability is to understand the radiation environment of the planet in the full spectral domain. We characterize the X-rays to mid-IR radiative properties of Proxima with the goal of providing the top-of-atmosphere fluxes on the planet. We also aim at constraining the fundamental properties of the star. We employ observations from a large number of facilities and make use of different methodologies to piece together the full spectral energy distribution of Proxima. In the high-energy domain, we pay particular attention to the contribution by rotational modulation, activity cycle, and flares so that the data provided are representative of the overall radiation dose received by the atmosphere of the planet. We present the full spectrum of Proxima covering 0.7 to 30000 nm. The integration of the data shows that the top-of-atmosphere average XUV irradiance on Proxima b is 0.293 W m^-2, i.e., nearly 60 times higher than Earth, and that the total irradiance is 877+/-44 W m^-2, or 64+/-3% of the solar constant but with a significantly redder spectrum. We also provide laws for the XUV evolution of Proxima corresponding to two scenarios. Regarding the fundamental properties of Proxima, we find M=0.120+/-0.003 Msun, R=0.146+/-0.007 Rsun, Teff=2980+/-80 K, and L=0.00151+/-0.00008 Lsun. In addition, our analysis reveals a ~20% excess in the 3-30 micron flux of the star that is best interpreted as arising from warm dust in the system. The data provided here should be useful to further investigate the current atmospheric properties of Proxima b as well as its past history, with the overall aim of firmly establishing the habitability of the planet.

Polarized Disk Emission from Herbig Ae/Be Stars Observed Using Gemini Planet Imager: HD 144432, HD 150193, HD 163296, and HD 169142

Abstract In order to look for signs of ongoing planet formation in young disks, we carried out the first J-band polarized emission imaging of the Herbig Ae/Be stars HD 150193, HD 163296, and HD 169142 using the Gemini Planet Imager, along with new H band observations of HD 144432. We confirm the complex “double ring” structure for the nearly face-on system HD 169142 first seen in H-band, finding the outer ring to be substantially redder than the inner one in polarized intensity. Using radiative transfer modeling, we developed a physical model that explains the full spectral energy distribution and J- and H-band surface brightness profiles, suggesting that the differential color of the two rings could come from reddened starlight traversing the inner wall and may not require differences in grain properties. In addition, we clearly detect an elongated, off-center ring in HD 163296 (MWC 275), locating the scattering surface to be 18 au above the midplane at a radial distance of 77 au, co-spatial with a ring seen at 1.3 mm by ALMA linked to the CO snow line. Lastly, we report a weak tentative detection of scattered light for HD 150193 (MWC 863) and a non-detection for HD 144432; the stellar companion known for each of these targets has likely disrupted the material in the outer disk of the primary star. For HD 163296 and HD 169142, the prominent outer rings we detect could be evidence for giant planet formation in the outer disk or a manifestation of large-scale dust growth processes possibly related to snow-line chemistry.

Characterizing elusive, faint dusty star-forming galaxies: a lensed, optically undetected ALMA galaxy atz ~ 3.3

We present the serendipitous ALMA detection of a faint submillimeter galaxy (SMG) lensed by a foreground z~1 galaxy. By optimizing the source detection to deblend the system, we accurately build the full spectral energy distribution of the distant galaxy from the I814 band to radio wavelengths. It is extremely red, with a I-K colour larger than 2.5. We estimate a photometric redshift of 3.28 and determine the physical parameters. The distant galaxy turns out to be magnified by the foreground lens by a factor of ~1.5, which implies an intrinsic Ks-band magnitude of ~24.5, a submillimeter flux at 870um of ~2.5 mJy and a SFR of ~150-300Msun/yr, depending on the adopted tracer. These values place our source towards the faint end of the distribution of observed SMGs, and in particular among the still few faint SMGs with a fully characterized spectral energy distribution, which allows us not only to accurately estimate its redshift but also to measure its stellar mass and other physical properties. The galaxy studied in this work is a representative of the population of faint SMGs, of which only few objects are known to date, that are undetected in optical and therefore are not typically accounted for when measuring the cosmic star formation history (SFH). This faint galaxy population thus likely represents an important and missing piece in our understanding of the cosmic SFH. Its observation and characterization is of major importance to achieve a solid picture of galaxy evolution.

G11.92−0.61 MM1: a Keplerian disc around a massive young proto-O star

The formation process of massive stars is not well understood, and advancement in our understanding benefits from high resolution observations and modelling of the gas and dust surrounding individual high-mass (proto)stars. Here we report sub-arcsecond (<1550 au) resolution observations of the young massive star G11.92-0.61 MM1 with the SMA and VLA. Our 1.3 mm SMA observations reveal consistent velocity gradients in compact molecular line emission from species such as CH$_3$CN, CH$_3$OH, OCS, HNCO, H$_2$CO, DCN and CH$_3$CH$_2$CN, oriented perpendicular to the previously reported bipolar molecular outflow from MM1. Modelling of the compact gas kinematics suggests a structure undergoing rotation around the peak of the dust continuum emission. The rotational profile can be well fit by a model of a Keplerian disc, including infall, surrounding an enclosed mass of 30-60M$_{\odot}$, of which 2-3M$_{\odot}$ is attributed to the disc. From modelling the CH$_3$CN emission, we determine that two temperature components, of 150 K and 230 K, are required to adequately reproduce the spectra. Our 0.9 and 3.0cm VLA continuum data exhibit an excess above the level expected from dust emission; the full centimetre-submillimetre wavelength spectral energy distribution of MM1 is well reproduced by a model including dust emission, an unresolved hypercompact H{\i}{\i} region, and a compact ionised jet. In combination, our results suggest that MM1 is an example of a massive proto-O star forming via disc accretion, in a similar way to that of lower mass stars.

TheHerschelVirgo Cluster Survey

The Star formation rate (SFR) is a crucial parameter to investigate galaxy evolution. At low redshift the cosmic SFR density declines smoothly, and massive active galaxies become passive, reducing their star formation activity. This implies that the bulk of the SFR density at low redshift is mainly driven by low mass objects. We investigate the properties of a sample of low luminosity Far-Infrared (FIR) sources selected at 250 microns from Pappalardo et al. (2015). We have collected data from Ultraviolet to FIR to perform a multi-wavelengths analysis. The main goal is to investigate the correlation between SFR, stellar mass, and dust mass for a galaxy population with a wide range in dust content and stellar mass, including the low mass regime that most probably dominates the SFR density at low z. We define a main sample of ~800 sources with full Spectral Energy Distribution (SED) coverage between 0.15 < lambda < 500 microns and an extended sample with ~5000 sources in which we remove the constraints on the Ultraviolet and Near-Infrared bands. We analyze both samples with two different SED fitting methods: MAGPHYS and CIGALE. In the SFR versus stellar mass plane our samples occupy a region included between local spirals and higher redshift star forming galaxies. The galaxies subsample with the higher masses (M* > 3e10 Msol) does not lie on the main sequence, but shows a small offset, as a consequence of the decreased star formation. Low mass galaxies (M* < 1e10 Msol) settle in the main sequence with SFR and stellar mass consistent with local spirals. Deep Herschel data allow the identification of a mixed galaxy population, with galaxies still in an assembly phase, or galaxies at the beginning of their passive evolution. We find that the dust luminosity is the parameter that discriminates these two galaxy populations.

THE MOSDEF SURVEY: THE STRONG AGREEMENT BETWEEN Hα AND UV-TO-FIR STAR FORMATION RATES FOR z ∼ 2 STAR-FORMING GALAXIES*

ABSTRACT We present the first direct comparison between Balmer line and panchromatic spectral energy distribution (SED)-based star formation rates (SFRs) for z &sim; 2 ?> galaxies. For this comparison, we used 17 star-forming galaxies selected from the MOSFIRE Deep Evolution Field (MOSDEF) survey, with 3 &sgr; ?> detections for Hα and at least two IR bands (Spitzer/MIPS 24 μm and Herschel/PACS 100 and 160 μm, and in some cases Herschel/SPIRE 250, 350, and 500 μm). The galaxies have total IR (8–1000 μm) luminosities of &sim; 10 11.4 &ndash; 10 12.4 L &CircleDot; ?> and SFRs of &sim; 30 &ndash; 250 M &CircleDot; yr &minus; 1 ?> . We fit the UV-to-far-IR SEDs with flexible stellar population synthesis (FSPS) models—which include both stellar and dust emission—and compare the inferred SFRs with the SFR(Hα, Hβ) values corrected for dust attenuation using Balmer decrements. The two SFRs agree with a scatter of 0.17 dex. Our results imply that the Balmer decrement accurately predicts the obscuration of the nebular lines and can be used to robustly calculate SFRs for star-forming galaxies at z &sim; 2 ?> with SFRs up to &sim; 200 M &CircleDot; yr &minus; 1 ?> . We also use our data to assess SFR indicators based on modeling the UV-to-mid-IR SEDs or by adding SFR(UV) and SFR(IR), for which the latter is based on the mid-IR only or on the full IR SED. All these SFRs show a poorer agreement with SFR(Hα, Hβ) and in some cases large systematic biases are observed. Finally, we show that the SFR and dust attenuation derived from the UV-to-near-IR SED alone are unbiased when assuming a delayed exponentially declining star formation history.