Emission In Star-forming Galaxies Research Articles

DEVILS/MIGHTEE/GAMA/DINGO: the impact of SFR time-scales on the SFR-radio luminosity correlation

ABSTRACT The tight relationship between infrared luminosity (LTIR) and 1.4 GHz radio continuum luminosity ($L_\mathrm{1.4\, GHz}$) has proven useful for understanding star formation free from dust obscuration. Infrared emission in star-forming galaxies typically arises from recently formed, dust-enshrouded stars, whereas radio synchrotron emission is expected from subsequent supernovae. By leveraging the wealth of ancillary far-ultraviolet – far-infrared photometry from the Deep Extragalactic VIsible Legacy Survey and Galaxy and Mass Assembly surveys, combined with 1.4 GHz observations from the Meer Karoo Array Telescope International GHz Tiered Extragalactic Exploration survey and Deep Investigation of Neutral Gas Origin projects, we investigate the impact of time-scale differences between far-ultraviolet – far-infrared and radio-derived star formation rate (SFR) tracers. We examine how the spectral energy distribution (SED)-derived star formation histories (SFHs) of galaxies can be used to explain discrepancies in these SFR tracers, which are sensitive to different time-scales. Galaxies exhibiting an increasing SFH have systematically higher LTIR and SED-derived SFRs than predicted from their 1.4 GHz radio luminosity. This indicates that insufficient time has passed for subsequent supernovae-driven radio emission to accumulate. We show that backtracking the SFR(t) of galaxies along their SED-derived SFHs to a time several hundred megayears prior to their observed epoch will both linearize the SFR–$L_\mathrm{1.4\, GHz}$ relation and reduce the overall scatter. The minimum scatter in the SFR(t)–$L_\mathrm{1.4\, GHz}$ is reached at 200 – 300 Myr prior, consistent with theoretical predictions for the time-scales required to disperse the cosmic ray electrons responsible for the synchrotron emission.

Early Results from GLASS-JWST. VI. Extreme Rest-optical Equivalent Widths Detected in NIRISS Wide Field Slitless Spectroscopy

Wide Field Slitless Spectroscopy (WFSS) provides a powerful tool for detecting strong line emission in star-forming galaxies (SFGs) without the need for target preselection. As part of the GLASS-JWST Early Release Science (ERS) program, we leverage the near-infrared wavelength capabilities of NIRISS (1–2.2 μm) to observe rest-optical emission lines out to z ∼ 3.4, to a depth and with a spatial resolution higher than ever before (Hα to z < 2.4; [O iii]+Hβ to z < 3.4). In this Letter we constrain the rest-frame [O III]λ5007 equivalent width (EW) distribution for a sample of 76 1 < z < 3.4 SFGs in the A2744 Hubble Frontier Field and determine an abundance fraction of extreme emission line galaxies with EW > 750Å in our sample to be 12%. We determine a strong correlation between the measured Hβ and [O III]λ5007 EWs, supporting that the high [O III]λ5007 EW objects require massive stars in young stellar populations to generate the high-energy photons needed to doubly ionize oxygen. We extracted spectra for objects up to 2 mag fainter in the near-infrared than previous WFSS studies with the Hubble Space Telescope. Thus, this work clearly highlights the potential of JWST/NIRISS to provide high-quality WFSS data sets in crowded cluster environments.

A new look at the infrared properties of z ∼ 5 galaxies

ABSTRACT Recent Atacama Large Millimeter Array large surveys unveiled the presence of significant dust continuum emission in star-forming galaxies at z &amp;gt; 4. Unfortunately, such large programs – i.e. ALPINE (z ∼ 5) and REBELS (z ∼ 7) – only provide us with a single far-infrared (FIR) continuum data point for their individual targets. Therefore, high-z galaxies FIR spectral energy densities (SEDs) remain mostly unconstrained, hinging on an assumption for their dust temperature (Td) in the SED fitting procedure. This introduces uncertainties in the inferred dust masses (Md), infrared luminosities (LIR), and obscured star formation rate (SFR) fraction at z &amp;gt; 4. In this work, we use a method that allows us to constrain Td with a single-band measurement by combining the 158 $\mu$m continuum information with the overlying [C ii emission line. We analyse the 21 [C ii and FIR continuum-detected z ∼ 5 galaxies in ALPINE, finding a range of Td = 25–60 K and Md = 0.6–25.1 × 107 M⊙. Given the measured stellar masses of ALPINE galaxies, the inferred dust yields are around Md/M⋆ = (0.2–8) × 10−3, consistent with theoretical dust-production constraints. We find that eight out of the 21 ALPINE galaxies have LIR ≥ 1012 L⊙, comparable to ultraluminous IR galaxies (ULIRGs). Relying on ultraviolet-to-optical SED fitting, the SFR was underestimated by up to two orders of magnitude in four of these eight ULIRGs-like galaxies. We conclude that these four peculiar sources should be characterized by a two-phase interstellar medium structure with ‘spatially segregated’ FIR and ultraviolet emitting regions.

Inverse-Compton scattering of the cosmic infrared background

The thermal Sunyaev-Zel'dovich (tSZ) effect is the distortion generated in the cosmic microwave background (CMB) spectrum by the inverse-Compton scattering of CMB photons off free, energetic electrons, primarily located in the intracluster medium. Cosmic infrared background (CIB) photons from thermal dust emission in star-forming galaxies are expected to undergo the same process. In this work, we perform the first calculation of the resulting tSZ-like distortion in the CIB. Focusing on the CIB monopole, we use a halo model approach to calculate both the CIB signal and the Compton-$y$ field that generates the distortion. We self-consistently account for the redshift coevolution of the CIB and Compton-$y$ fields: they are (partially) sourced by the same dark matter halos, which introduces new aspects to the calculation as compared to the CMB case. We find that the inverse-Compton distortion to the CIB monopole spectrum has a positive (negative) peak amplitude of $\ensuremath{\approx}4\text{ }\text{ }\mathrm{Jy}/\mathrm{sr}$ ($\ensuremath{\approx}\ensuremath{-}5\text{ }\text{ }\mathrm{Jy}/\mathrm{sr}$) at 2260 GHz (940 GHz). In contrast to the usual tSZ effect, the distortion to the CIB spectrum has two null frequencies, at approximately 196 and 1490 GHz. We perform a Fisher matrix calculation to forecast the detectability of this new distortion signal by future experiments. PIXIE would have sufficient instrumental sensitivity to detect the signal at $4\ensuremath{\sigma}$, but foreground contamination reduces the projected signal-to-noise by a factor of $\ensuremath{\approx}70$. A future ESA Voyage 2050 spectrometer could detect the CIB distortion at $\ensuremath{\approx}5\ensuremath{\sigma}$ significance, even after marginalizing over foregrounds. A measurement of this signal would provide new information on the star formation history of the Universe, and the distortion anisotropies may be accessible by near-future ground-based experiments.

Simulating radio synchrotron emission in star-forming galaxies: small-scale magnetic dynamo and the origin of the far-infrared–radio correlation

ABSTRACT In star-forming galaxies, the far-infrared (FIR) and radio-continuum luminosities obey a tight empirical relation over a large range of star-formation rates (SFR). To understand the physics, we examine magnetohydrodynamic galaxy simulations, which follow the genesis of cosmic ray (CR) protons at supernovae and their advective and anisotropic diffusive transport. We show that gravitational collapse of the proto-galaxy generates a corrugated accretion shock, which injects turbulence and drives a small-scale magnetic dynamo. As the shock propagates outwards and the associated turbulence decays, the large velocity shear between the supersonically rotating cool disc with respect to the (partially) pressure-supported hot circumgalactic medium excites Kelvin–Helmholtz surface and body modes. Those interact non-linearly, inject additional turbulence and continuously drive multiple small-scale dynamos, which exponentially amplify weak seed magnetic fields. After saturation at small scales, they grow in scale to reach equipartition with thermal and CR energies in Milky Way-mass galaxies. In small galaxies, the magnetic energy saturates at the turbulent energy while it fails to reach equipartition with thermal and CR energies. We solve for steady-state spectra of CR protons, secondary electrons/positrons from hadronic CR-proton interactions with the interstellar medium, and primary shock-accelerated electrons at supernovae. The radio-synchrotron emission is dominated by primary electrons, irradiates the magnetized disc and bulge of our simulated Milky Way-mass galaxy and weakly traces bubble-shaped magnetically loaded outflows. Our star-forming and star-bursting galaxies with saturated magnetic fields match the global FIR-radio correlation (FRC) across four orders of magnitude. Its intrinsic scatter arises due to (i) different magnetic saturation levels that result from different seed magnetic fields, (ii) different radio synchrotron luminosities for different specific SFRs at fixed SFR, and (iii) a varying radio intensity with galactic inclination. In agreement with observations, several 100-pc-sized regions within star-forming galaxies also obey the FRC, while the centres of starbursts substantially exceed the FRC.

Ionization of He II in star-forming galaxies by X-rays from cluster winds and superbubbles

The nature of the sources powering nebular He II emission in star-forming galaxies remains debated, and various types of objects have been considered, including Wolf-Rayet stars, X-ray binaries, and Population III stars. Modern X-ray observations show the ubiquitous presence of hot gas filling star-forming galaxies. We use a collisional ionization plasma code to compute the specific He II ionizing flux produced by hot gas and show that if its temperature is not too high (≲2.5 MK), then the observed levels of soft diffuse X-ray radiation could explain He II ionization in galaxies. To gain a physical understanding of this result, we propose a model that combines the hydrodynamics of cluster winds and hot superbubbles with observed populations of young massive clusters in galaxies. We find that in low-metallicity galaxies, the temperature of hot gas is lower and the production rate of He II ionizing photons is higher compared to high-metallicity galaxies. The reason is that the slower stellar winds of massive stars in lower-metallicity galaxies input less mechanical energy in the ambient medium. Furthermore, we show that ensembles of star clusters up to ∼10−20 Myr old in galaxies can produce enough soft X-rays to induce nebular He II emission. We discuss observations of the template low-metallicity galaxy I Zw 18 and suggest that the He II nebula in this galaxy is powered by a hot superbubble. Finally, appreciating the complex nature of stellar feedback, we suggest that soft X-rays from hot superbubbles are among the dominant sources of He II ionizing flux in low-metallicity star-forming galaxies.

The evolution of the low-frequency radio AGN population to z ≃ 1.5 in the ELAIS N1 field

ABSTRACT We study the cosmic evolution of radio sources out to z ≃ 1.5 using a GMRT 610 MHz survey covering ∼1.86 deg2 of the ELAIS N1 field with a minimum/median rms noise 7.1/19.5 μJy beam−1 and an angular resolution of 6 arcsec. We classify sources as star forming galaxies (SFGs), radio-quiet (RQ) and radio-loud (RL) Active Galactic Nuclei (AGNs) using a combination of multiwavelength diagnostics and find evidence in support of the radio emission in SFGs and RQ AGN arising from star formation, rather than AGN-related processes. At high luminosities, however, both SFGs and RQ AGN display a radio excess when comparing radio and infrared star formation rates. The vast majority of our sample lie along the $\rm {SFR - \mathit{ M}_{\star }}$ ‘main sequence’ at all redshifts when using infrared star formation rates. We derive the 610 MHz radio luminosity function for the total AGN population, constraining its evolution via continuous models of pure density and pure luminosity evolution with $\rm {\Phi ^{\star }\, \propto \, (\, 1+\, \mathit{ z})^{(2.25\pm 0.38)-(0.63\pm 0.35)z}}$ and $\rm {\mathit{ L}_{610\, MHz}\, \propto \, (\, 1+\, \mathit{ z})^{(3.45\pm 0.53)-(0.55\pm 0.29)\mathit{ z}}}$, respectively. For our RQ and RL AGN, we find a fairly mild evolution with redshift best fitted by pure luminosity evolution with $\rm {\mathit{ L}_{610\, MHz}\, \propto \, (\, 1+\, \mathit{ z})^{(2.81\pm 0.43)-(0.57\pm 0.30)\mathit{ z}}}$ for RQ AGN and $\rm {\mathit{ L}_{610\, MHz}\, \propto \, (\, 1+\, \mathit{ z})^{(3.58\pm 0.54)-(0.56\pm 0.29)\mathit{ z}}}$ for RL AGN. The 610 MHz radio AGN population thus comprises two differently evolving populations whose radio emission is mostly SF-driven or AGN-driven, respectively.

Properties of galaxies at z ≈ 7 – 9 revealed by ALMA

AbstractUnderstanding properties of galaxies in the epoch of reionization (EoR) is a frontier in the modern astronomy. With the advent of ALMA, it has become possible to detect far-infrared fine structure lines (e.g. [CII] 158 μm and [OIII] 88 μm) and dust continuum emission in star-forming galaxies in the EoR. Among these lines, our team is focusing on [OIII] 88 μm observations in high-z galaxies. After the first detection of [OIII] in the epoch of reionization (EoR) in 2016 from our team at z = 7.21, there are now more than ten [OIII] detections at z &gt; 6 up to z = 9.11. Interestingly, high-z galaxies typically have very high [OIII]-to-[CII] luminosity ratio ranging from 3 to 12 or higher, demonstrating [OIII] is a powerful tracer at high-z. The high luminosity ratios may imply that high-z galaxies have low gas-phase metallicity and/or high ionization states.

Photometric identification and MMT spectroscopy of new extremely metal-poor galaxies: towards a better understanding of young stellar populations at low metallicity

Extremely metal-poor star-forming galaxies (XMPs) represent one of our only laboratories for study of the low-metallicity stars we expect to encounter at early epochs. But as our understanding of the $z>6$ universe has improved, it has become clear that the majority of known XMPs within 100 Mpc host significantly less prominent massive star populations than their reionization-era counterparts, severely limiting their utility as testbeds for interpreting spectral features found at the highest redshifts. Here we present a new photometric selection technique designed to identify nearby XMPs dominated by young stellar populations comparable to those expected in the reionization era. We apply our technique to uncover candidate XMPs in SDSS imaging at magnitudes $16<i'<23$, extending significantly below the completeness limits of the SDSS spectroscopic survey. Spectroscopic observations with the MMT confirm that 32 of the 53 uniformly metal-poor and high specific star formation rate targets we observed have gas-phase oxygen abundances $12+\log\mathrm{O/H}<7.7$ ($Z/Z_\odot<0.1$), including two in the range of the lowest-metallicity galaxies known, $Z/Z_\odot<0.05$. Our observations shed new light onto the longstanding mystery of He II emission in star-forming galaxies: we find that the equivalent width of the He II $\lambda 4686$ high-ionization emission line does not scale with that of H$\beta$ in our sample, suggesting that binary evolution or other processes on $>10$ Myr timescales contribute substantially to the $\mathrm{He^+}$-ionizing photon budget in this metallicity regime. Applying such selection techniques coupled with deep spectroscopy to next-generation photometric surveys like LSST may eventually provide a basis for an empirical understanding of metal-poor massive stars.

What is driving the evolution of the far-infrared radio correlation?

Far infrared-radio correlation represents a linear relationship between far-infrared (FIR) and radio emission in star-forming galaxies. Previous observations have confirmed that this correlation is maintained over a large range of redshift and does not evolve, although a small dispersion is present. However, some of more recent observations at high redshift have shown the opposite. The question that arises is - what is driving this evolution? In this paper we investigate the possibility that galaxy morphology is the answer to this question. A sample of 37 submillimeter galaxies (SMGs) is analyzed. The observation and morphological class of these galaxies has previously been published. We examined FIR-radio correlation in galaxies of different morphological type in this sample and found that for star-forming disk galaxies correlation is stable and does not evolve and for irregular and interacting galaxies we find some hints of evolution.

C iii] Emission in Star-forming Galaxies at z ∼ 1

Abstract The C iii]λλ1907, 1909 rest-frame UV emission doublet has recently been detected in galaxies during the epoch of reionization (z &gt; 6), with a high equivalent width (EW; 10 Å, rest frame). Currently, it is possible to obtain much more detailed information for star-forming galaxies at significantly lower redshift. Accordingly, studies of their far-UV spectra are useful for understanding the factors modulating the strength of C iii] emission. We present the first statistical sample of C iii] emission measurements in star-forming galaxies at z ∼ 1. Our sample is drawn from the DEEP2 survey and spans the redshifts 0.64 z 1.35 ( ). We find that the median EW of individual C iii] detections in our sample (1.30 Å) is much smaller than the typical value observed thus far at z &gt; 6. Furthermore, out of 184 galaxies with coverage of C iii], only 40 have significant detections. Galaxies with individual C iii] detections have bluer colors and lower luminosities on average than those without, implying that strong C iii] emitters are in general young and low-mass galaxies without significant dust extinction. Using stacked spectra, we further investigate how C iii] strength correlates with multiple galaxy properties (M B , U − B, M *, star formation rate, specific star formation rate) and rest-frame near-UV (Fe ii* and Mg ii) and optical ([O iii] and Hβ) emission line strengths. These results provide a detailed picture of the physical environment in star-forming galaxies at z ∼ 1, and motivate future observations of strong C iii] emitters at similar redshifts.

Simultaneously modelling far-infrared dust emission and its relation to CO emission in star-forming galaxies

We present a method to simultaneously model the dust far-infrared spectral energy distribution (SED) and the total infrared $-$ carbon monoxide (CO) integrated intensity $(S_{\rm IR}-I_{\rm CO})$ relationship. The modelling employs a hierarchical Bayesian (HB) technique to estimate the dust surface density, temperature ($T_{\rm eff}$), and spectral index at each pixel from the observed far-infrared (FIR) maps. Additionally, given the corresponding CO map, the method simultaneously estimates the slope and intercept between the FIR and CO intensities, which are global properties of the observed source. The model accounts for correlated and uncorrelated uncertainties, such as those present in Herschel observations. Using synthetic datasets, we demonstrate the accuracy of the HB method, and contrast the results with common non-hierarchical fitting methods. As an initial application, we model the dust and gas on 100 pc scales in the Magellanic Clouds from Herschel FIR and NANTEN CO observations. The slopes of the $\log S_{\rm IR}-\log I_{\rm CO}$ relationship are similar in both galaxies, falling in the range 1.1$-$1.7. However, in the SMC the intercept is nearly 3 times higher, which can be explained by its lower metallicity than the LMC, resulting in a larger $S_{\rm IR}$ per unit $I_{\rm CO}$. The HB modelling evidences an increase in $T_{\rm eff}$ in regions with the highest $I_{\rm CO}$ in the LMC. This may be due to enhanced dust heating in the densest molecular regions from young stars. Such simultaneous dust and gas modelling may reveal variations in the properties of the ISM and its association with other galactic characteristics, such as star formation rates and/or metallicities.

Narrow He II emission in star-forming galaxies at low metallicity

Context. In a recent study, star-forming galaxies with He ii λ1640 emission at moderate redshifts between 2 and 4.6 have been found to occur in two modes that are distinguished by the width of their He ii emission lines. Broad He ii emission has been attributed to stellar emission from a population of evolved Wolf-Rayet (WR) stars. The origin of narrow He ii emission is less clear but has been attributed to nebular emission excited by a population of very hot Pop III stars formed in pockets of pristine gas at moderate redshifts.

THE EXTENDED He II λ 4686-EMITTING REGION IN IZw 18 UNVEILED: CLUES FOR PECULIAR IONIZING SOURCES

New integral field spectroscopy has been obtained for IZw18, the nearby lowest-metallicity galaxy considered our best local analog of systems forming at high-z. Here we report the spatially resolved spectral map of the nebular HeII4686 emission in IZw18, from which we derived for the first time its total HeII-ionizing flux. Nebular HeII emission implies the existence of a hard radiation field. HeII-emitters are observed to be more frequent among high-z galaxies than for local objects. So investigating the HeII-ionizing source(s) in IZw18 may reveal the ionization processes at high-z. HeII emission in star-forming galaxies, has been suggested to be mainly associated with Wolf-Rayet stars (WRs), but WRs cannot satisfactorily explain the HeII-ionization at all times, in particular at lowest metallicities. Shocks from supernova remnants, or X-ray binaries, have been proposed as additional potential sources of HeII-ionizing photons. Our data indicate that conventional HeII-ionizing sources (WRs, shocks, X-ray binaries) are not sufficient to explain the observed nebular HeII4686 emission in IZw18. We find that the HeII-ionizing radiation expected from models for either low-metallicity super-massive O stars or rotating metal-free stars could account for the HeII-ionization budget measured, while only the latter models could explain the highest values of HeII4686/Hbeta observed. The presence of such peculiar stars in IZw18 is suggestive and further investigation in this regard is needed. This letter highlights that some of the clues of the early Universe can be found here in our cosmic backyard.

The sub-mJy radio sky in the Extended Chandra Deep Field-South: source population

The sub-mJy radio population is a mixture of active systems, that is star-forming galaxies (SFGs) and active galactic nuclei (AGNs). We study a sample of 883 radio sources detected at 1.4 GHz in a deep Very Large Array survey of the Extended Chandra Deep Field-South that reaches a best rms sensitivity of 6 μJy. We have used a simple scheme to disentangle SFGs, radio-quiet (RQ), and radio-loud (RL) AGNs based on the combination of radio data with Chandra X-ray data and mid-infrared observations from Spitzer. We find that at flux densities between about 30 and 100 μJy, the radio population is dominated by SFGs (∼60 per cent) and that RQ AGNs become increasingly important over RL ones below 100 μJy. We also compare the host galaxy properties of the three classes in terms of morphology, optical colours and stellar masses. Our results show that both SFG and RQ AGN host galaxies have blue colours and late-type morphology while RL AGNs tend to be hosted by massive red galaxies with early-type morphology. This supports the hypothesis that radio emission in SFGs and RQ AGNs mainly comes from the same physical process: star formation in the host galaxy.

ORIGIN OF 12 μm EMISSION ACROSS GALAXY POPULATIONS FROMWISEAND SDSS SURVEYS

We cross-matched Wide-field Infrared Survey Explorer (WISE) sources brighter than 1 mJy at 12um with the Sloan Digital Sky Survey (SDSS) galaxy spectroscopic catalog to produce a sample of ~10^5 galaxies at <z>=0.08, the largest of its kind. This sample is dominated (70%) by star-forming (SF) galaxies from the blue sequence, with total IR luminosities in the range ~10^8-10^12 L_sun. We identify which stellar populations are responsible for most of the 12um emission. We find that most (~80%) of the 12um emission in SF galaxies is produced by stellar populations younger than 0.6 Gyr. In contrast, the 12um emission in weak AGN (L[OIII]<10^7 L_sun) is produced by older stars, with ages of ~1-3 Gyr. We find that L_[12um] linearly correlates with stellar mass for SF galaxies. At fixed 12um luminosity, weak AGN deviate toward higher masses since they tend to be hosted by massive, early-type galaxies with older stellar populations. Star-forming galaxies and weak AGN follow different L_[12um]-SFR (star formation rate) relations, with weak AGN showing excess 12um emission at low SFR (~0.02-1 M_sun/yr). This is likely due to dust grains heated by older stars. While the specific star formation rate (SSFR) of SF galaxies is nearly constant, the SSFR of weak AGN decreases by ~3 orders of magnitude, reflecting the very different star formation efficiencies between SF galaxies and massive, early-type galaxies. Stronger type II AGN in our sample (L_[OIII]>10^7 L_sun), act as an extension of massive SF galaxies, connecting the SF and weak AGN sequences. This suggests a picture where galaxies form stars normally until an AGN (possibly after a starburst episode) starts to gradually quench the SF activity. We also find that 4.6-12um color is a useful first-order indicator of SF activity in a galaxy when no other data are available.

DETECTION OF GAMMA-RAY EMISSION FROM THE STARBURST GALAXIES M82 AND NGC 253 WITH THE LARGE AREA TELESCOPE ON FERMI

We report the detection of high-energy gamma-ray emission from two starburst galaxies using data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Steady point-like emission above 200 MeV has been detected at significance levels of 6.8 sigma and 4.8 sigma respectively, from sources positionally coincident with locations of the starburst galaxies M82 and NGC 253. The total fluxes of the sources are consistent with gamma-ray emission originating from the interaction of cosmic rays with local interstellar gas and radiation fields and constitute evidence for a link between massive star formation and gamma-ray emission in star-forming galaxies.

Ultraviolet–to–Far‐Infrared Properties of Local Star‐forming Galaxies

We present the results of a multiwavelength study of nearby galaxies aimed at understanding the relation between the ultraviolet and far-infrared emission in star-forming galaxies. The data set comprises new ultraviolet (from HST STIS), ground-based Hα, and radio continuum observations, together with archival infrared data (from IRAS and ISO). The local galaxies are used as benchmarks for comparison of the infrared-to-ultraviolet properties with two populations of high-redshift galaxies: the submillimeter star-forming galaxies detected by SCUBA and the ultraviolet-selected Lyman break galaxies (LBGs). In addition, the long wavelength baseline covered by the present data enables us to compare the star formation rates (SFRs) derived from the observed ultraviolet, Hα, infrared, and radio luminosities and to gauge the impact of dust opacity in the local galaxies. We also derive a new calibration for the nonthermal part of the radio SFR estimator, based on the comparison of 1.4 GHz measurements with a new estimator of the bolometric luminosity of the star-forming regions. We find that more actively star-forming galaxies show higher dust opacities, which is in line with previous results. We find that the local star-forming galaxies have a lower Fλ(205 μm)/Fλ(UV) ratio by 2-3 orders of magnitude than the submillimeter-selected galaxies and may have a similar or somewhat higher Fλ(205 μm)/Fλ(UV) ratio than LBGs. The Fλ(205 μm)/Fλ(UV) ratio of the local galaxy population may be influenced by the cool dust emission in the far-infrared heated by nonionizing stellar populations, which may be reduced or absent in the LBGs.

The evolution of superbubbles and the detection of Ly in star-forming galaxies

The detection of Lyα emission in star-forming galaxies in different shapes and intensities (always smaller than predicted for case B recombination) has puzzled the astronomical community for more than a decade. Here we use two-dimensional calculations to follow the evolution of superbubbles and of the H ii regions generated by the output of UV photons from massive stars. We show the impact caused by massive star formation in the ISM of different galaxies and we look at the conditions required to detect Lyα emission from a nuclear H ii region, and the variety of profiles that may be expected as a function of time.