Measure Of Star Formation Rate Research Articles

Giant Biconical Dust Filaments in the Starburst Galaxy NGC 1808

We present the results from an analysis of multiwavelength archival data on the multiphase outflow in the starburst galaxy NGC 1808. We report the detection at 70 and 100 μm of dust filaments that extend up to ∼13 kpc from the galactic midplane and trace an edge-brightened biconical structure along the minor axis of the galaxy. The inner filaments are roughly cospatial with previously identified optical dust filaments, extraplanar polycyclic aromatic hydrocarbon emission, and neutral and ionized gaseous outflows. The 70/160 μm flux ratio, a proxy for the dust temperature, is elevated along the edges of the cones, indicating that the dusty medium has been driven out of the central regions of these cones and is possibly shock-heated by a large-scale outflow. We establish lower limits on the extraplanar dust mass and mean height above the stellar disk of log(Md/M⊙)=6.48 and ∣ z ∣ ∼ 5 kpc. The energy requirement of (5.1–9.6) × 1056 erg needed to lift the dusty material, assuming a Milky Way–like dust-to-gas ratio, can be supplied by the current starburst, with a measured star formation rate of 3.5–5.4 M ⊙ yr−1 over a timescale of (4–26) ξ −1 Myr, where ξ is the efficiency of energy transfer. We conclude that a starburst-driven outflow is the most likely mechanism by which the dust features were formed.

MUSEQuBES: mapping the distribution of neutral hydrogen around low-redshift galaxies

ABSTRACT We present a detailed study of cool, neutral gas traced by Lyα around 4595 z < 0.5 galaxies using stacks of background quasar spectra. The galaxies are selected from our MUSEQuBES low-z survey along with data from the literature. These galaxies, with a median stellar mass of ${\rm log}_{10}(M_*/\rm {\rm M}_{\odot })$ =10.0, are probed by 184 background quasars giving rise to 5054 quasar-galaxy pairs. The median impact parameter is b = 1.5 pMpc (median b/Rvir = 10.4) with 204 (419) quasar-galaxy pairs probing b/Rvir < 1(2). We find excess absorption out to at least ≈15Rvir transverse distance and ≈±600 $\rm km~s^{-1}$ along the line of sight. We show that the median stacked profile for the full sample, dominated by the pairs with b > Rvir, can be explained by a galaxy-absorber two-point correlation function with r0 = 7.6 pMpc and γ = −1.57. There are strong indications that the inner regions (≲Rvir) of the rest equivalent width profile are better explained by a log-linear (or a Gaussian) relation, whereas the outer regions are well described by a power-law, consistent with galaxy-absorber large-scale clustering. Using a sub-sample of 339 galaxies (442 quasar-galaxy pairs, median b/Rvir = 1.6) with star formation rate measurements, we find that the Lyα absorption is significantly stronger for star-forming galaxies compared to passive galaxies, but only within the virial radius. The Lyα absorption at b ≈ Rvir for a redshift-controlled sample peaks at $M_* \sim 10^9~ {\rm {\rm M}_{\odot }}~ (M_{\rm halo} \sim 10^{11}~ \rm {\rm M}_{\odot })$.

Probing supermassive black hole growth and its dependence on stellar mass and star formation rate in low-redshift galaxies

ABSTRACT We present an improved study of the relation between supermassive black hole growth and their host galaxy properties in the local Universe (z < 0.33). To this end, we build an extensive sample combining spectroscopic measurements of star formation rate (SFR) and stellar mass from Sloan Digital Sky Survey, with specific Black Hole accretion rate (sBHAR, $\lambda _{\mathrm{sBHAR}} \propto L_{\rm X}/\mathcal {M}_{\ast }$) derived from the XMM–Newton Serendipitous Source Catalogue (3XMM–DR8) and the Chandra Source Catalogue (CSC2.0). We find that the sBHAR probability distribution for both star-forming and quiescent galaxies has a power-law shape peaking at log λsBHAR ∼ −3.5 and declining towards lower sBHAR in all stellar mass ranges. This finding confirms the decrease of active galactic nucleus (AGN) activity in the local Universe compared to higher redshifts. We observe a significant correlation between $\log \, \lambda _{\rm sBHAR}$ and $\log \, {\rm SFR}$ in almost all stellar mass ranges, but the relation is shallower compared to higher redshifts, indicating a reduced availability of accreting material in the local Universe. At the same time, the BHAR-to-SFR ratio for star-forming galaxies strongly correlates with stellar mass, supporting the scenario where both AGN activity and stellar formation primarily depend on the stellar mass via fuelling by a common gas reservoir. Conversely, this ratio remains constant for quiescent galaxies, possibly indicating the existence of the different physical mechanisms responsible for AGN fuelling or different accretion mode in quiescent galaxies.

Exploring the physical properties of lensed star-forming clumps at 2 ≲ z ≲ 6

ABSTRACT We study the physical properties (size, stellar mass, luminosity, and star formation rate) and scaling relations for a sample of 166 star-forming clumps with redshift z ∼ 2–6.2. They are magnified by the Hubble Frontier Field galaxy cluster MACS J0416 and have robust lensing magnification (2 ≲ μ ≲ 82) computed by using our high-precision lens model, based on 182 multiple images. Our sample extends by ∼3 times the number of spectroscopically confirmed lensed clumps at z ≳ 2. We identify clumps in ultraviolet continuum images and find that, whenever the effective spatial resolution (enhanced by gravitational lensing) increases, they fragment into smaller entities, likely reflecting the hierarchically organized nature of star formation. Kpc-scale clumps, most commonly observed in field, are not found in our sample. The physical properties of our sample extend the parameter space typically probed by z ≳ 1 field observations and simulations, by populating the low mass (M⋆ ≲ 107 M⊙), low star formation rate (SFR ≲ 0.5 M⊙ yr−1), and small size (Reff ≲ 100 pc) regime. The new domain probed by our study approaches the regime of compact stellar complexes and star clusters. In the mass–size plane, our sample spans the region between galaxies and globular clusters, with a few clumps in the region populated by young star clusters and globular clusters. For the bulk of our sample, we measure star formation rates which are higher than those observed locally in compact stellar systems, indicating different conditions for star formation at high redshift than in the local Universe.

The Distribution of UV Radiation Field in the Molecular Clouds of Gould Belt

The distribution of ultraviolet (UV) radiation field provides critical constraints on the physical environments of molecular clouds. Within 1 kpc of our solar system and fostering protostars of different masses, the giant molecular clouds in the Gould Belt present an excellent opportunity to resolve the UV field structure in star-forming regions. We performed spectral energy distribution (SED) fitting of the archival data from the Herschel Gould Belt Survey (HGBS). Dust radiative transfer analysis with the DUSTY code was applied to 23 regions in 14 molecular complexes of the Gould Belt, resulting in the spatial distribution of the radiation field in these regions. For 10 of 15 regions with independent measurements of star formation rate, their star formation rate and UV radiation intensity largely conform to a linear correlation found in previous studies.

What is the origin of the stacked radio emission in radio-undetected quasars?

Radio emission in the brightest radio quasars can be attributed to processes inherent to active galactic nuclei (AGN) powered by super massive black holes (SMBHs), while the physical origins of the radio fluxes in quasars without radio detections have not been established with full certainly. Deep radio surveys carried out with the Low Frequency ARray (LOFAR) are at least one order of magnitude more sensitive for objects with typical synchrotron spectra than previous wide-area high-frequency surveys ( > 1.0 GHz). With the enhanced sensitivity that LOFAR offers, we investigate the radio-infrared continuum of LOFAR radio-detected quasars (RDQs) and LOFAR radio-undetected quasars (RUQs) in the 9.3 deg2NOAO Deep Wide-field survey (NDWFS) of the Boötes field; RUQs are quasars that are individually undetected at a level of ≥5σin the LOFAR observations. To probe the nature of the radio and infrared emission, where direct detection is not possible due to the flux density limits, we used a median image stacking procedure. This was done in the radio frequencies of 150 MHz, 325 MHz, 1.4 GHz and 3.0 GHz, and in nine infrared bands between 8 and 500 μm. The stacking analysis allows us to probe the radio-luminosity for quasars that are up to one order of magnitude fainter than the ones detected directly. The radio and infrared photometry allow us to derive the median spectral energy distributions of RDQs and RUQs in four contiguous redshift bins between 0 < z < 6.15. The infrared photometry is used to derive the infrared star-formation rate (SFR) through SED fitting, and is compared with two independent radio-based star-formation (SF) tracers using the far-infrared radio correlation (FIRC) of star-forming galaxies. We find a good agreement between our radio and infrared SFR measurements and the predictions of the FIRC. Moreover, we use the FIRC predictions to establish the level of the contribution due to SMBH accretion to the total radio-luminosity. We show that SMBH accretion can account for ∼5−41% of the total radio-luminosity in median RUQs, while for median RDQs the contribution is ∼50−84%. This implies that vigorous SF activity is coeval with SMBH growth in our median stacked quasars. We find that median RDQs have higher SFRs that agree well with those of massive star-forming main sequence galaxies, while median RUQs present lower SFRs than RDQs. Furthermore, the behavior of the radio-loudness parameter (R = log10(Lrad/LAGN)) is investigated. For quasars withR ≥ −4.5, the radio-emission is consistent with being dominated by SMBH accretion, while for low radio luminosity quasars withR < −4.5 the relative contribution of SF to the radio fluxes increases as the SMBH component becomes weaker. We also find signatures of SF suppression due to negative AGN feedback in the brightest median RDQs at 150 MHz. Finally, taking advantage of our broad spectral coverage, we studied the radio spectra of median RDQs and RUQs. The spectral indices of RUQs and RDQs do not evolve significantly with redshift, but they become flatter towards lower frequencies.

Infrared Spectral Energy Distributions and Dust Masses of Sub-solar Metallicity Galaxies at z ∼ 2.3

Abstract We present results from Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm continuum observations of a sample of 27 star-forming galaxies at z = 2.1–2.5 from the MOSFIRE Deep Evolution Field survey with metallicity and star formation rate measurements from optical emission lines. Using stacks of Spitzer, Herschel, and ALMA photometry (rest frame ∼8–400 μm), we examine the infrared (IR) spectral energy distributions (SED) of z ∼ 2.3 subsolar-metallicity (∼0.5 Z ⊙) luminous infrared galaxies (LIRGs). We find that the data agree well with an average template of higher-luminosity local low-metallicity dwarf galaxies (reduced χ 2 = 1.8). When compared with the commonly used templates for solar-metallicity local galaxies or high-redshift LIRGs and ultraluminous IR galaxies, even in the most favorable case (with reduced χ 2 = 2.8), the templates are rejected at >98% confidence. The broader and hotter IR SED of both the local dwarfs and high-redshift subsolar-metallicity galaxies may result from different grain properties or a harder/more intense ionizing radiation field that increases the dust temperature. The obscured star formation rate (SFR) indicated by the far-IR emission of the subsolar-metallicity galaxies is only ∼60% of the total SFR, considerably lower than that of the local LIRGs with ∼96%–97% obscured fractions. Due to the evolving IR SED shape, the local LIRG templates fit to mid-IR data overestimate the Rayleigh–Jeans tail measurements by a factor of 2–20. These templates underestimate IR luminosities if fit to the observed ALMA fluxes by >0.4 dex. At a given stellar mass or metallicity, dust masses at z ∼ 2.3 are an order of magnitude higher than z ∼ 0. Given the predicted molecular gas fractions, the observed z ∼ 2.3 dust-to-stellar mass ratios suggest lower dust-to-molecular gas masses than in local galaxies with similar metallicities.

The Mass–Metallicity Relation at z ∼ 1–2 and Its Dependence on the Star Formation Rate

Abstract We present a new measurement of the gas-phase mass–metallicity relation (MZR) and its dependence on star formation rates (SFRs) at 1.3 < z < 2.3. Our sample comprises 1056 galaxies with a mean redshift of z = 1.9, identified from the Hubble Space Telescope Wide Field Camera 3 (WFC3) grism spectroscopy in the Cosmic Assembly Near-infrared Deep Extragalactic Survey and the WFC3 Infrared Spectroscopic Parallel Survey. This sample is four times larger than previous metallicity surveys at z ∼ 2 and reaches an order of magnitude lower in stellar mass (108 M ⊙). Using stacked spectra, we find that the MZR evolves by 0.3 dex relative to z ∼ 0.1. Additionally, we identify a subset of 49 galaxies with high signal-to-noise (S/N) spectra and redshifts between 1.3 < z < 1.5, where Hα emission is observed along with [O iii] and [O ii]. With accurate measurements of SFR in these objects, we confirm the existence of a mass–metallicity–SFR (M–Z–SFR) relation at high redshifts. These galaxies show systematic differences from the local M–Z–SFR relation, which vary depending on the adopted measurement of the local relation. However, it remains difficult to ascertain whether these differences could be due to redshift evolution, as the local M–Z–SFR relation is poorly constrained at the masses and SFRs of our sample. Lastly, we reproduced our sample selection in the IllustrisTNG hydrodynamical simulation, demonstrating that our line flux limit lowers the normalization of the simulated MZR by 0.2 dex. We show that the M–Z–SFR relation in IllustrisTNG has an SFR dependence that is too steep by a factor of around 3.

The impact of ionized outflows from z ∼ 2.5 quasars is not through instantaneous in situ quenching: the evidence from ALMA and VLT/SINFONI

ABSTRACT We present high-resolution (∼2.4 kpc) ALMA band 7 observations (rest-frame λ ∼ 250 $\mu$m) of three powerful z ∼ 2.5 quasars (Lbol = 1047.3–1047.5 erg s−1). These targets have previously been reported as showing evidence for suppressed star formation based on cavities in the narrow H α emission at the location of outflows traced with [O iii] emission. Here, we combine the ALMA observations with a re-analysis of the VLT/SINFONI data to map the rest-frame far-infrared emission, H α emission, and [O iii] emission. In all targets, we observe high velocity [O iii] gas (i.e. W80 ∼ 1000–2000 km s−1) across the whole galaxy. We do not identify any H α emission that is free from contamination from AGN-related processes; however, based on SED analyses, we show that the ALMA data contain a significant dust-obscured star formation component in two out of the three systems. This dust emission is found to be extended over ≈1.5–5.5 kpc in the nuclear regions, overlaps with the previously reported H α cavities and is co-spatial with the peak in surface brightness of the [O iii] outflows. In summary, within the resolution and sensitivity limits of the data, we do not see any evidence for a instantaneous shut down of in situ star formation caused directly by the outflows. However, similar to the conclusions of previous studies and based on our measured star formation rates, we do not rule out that the global host galaxy star formation could be suppressed on longer time-scales by the cumulative effect of quasar episodes during the growth of these massive black holes.

The infrared-radio correlation of star-forming galaxies is stronglyM⋆-dependent but nearly redshift-invariant sincez∼ 4

Over the past decade, several works have used the ratio between total (rest 8−1000μm) infrared and radio (rest 1.4 GHz) luminosity in star-forming galaxies (qIR), often referred to as the infrared-radio correlation (IRRC), to calibrate the radio emission as a star formation rate (SFR) indicator. Previous studies constrained the evolution ofqIRwith redshift, finding a mild but significant decline that is yet to be understood. Here, for the first time, we calibrateqIRas a function ofbothstellar mass (M⋆) and redshift, starting from anM⋆-selected sample of > 400 000 star-forming galaxies in the COSMOS field, identified via (NUV − r)/(r − J) colours, at redshifts of 0.1 < z < 4.5. Within each (M⋆,z) bin, we stacked the deepest available infrared/sub-mm and radio images. We fit the stacked IR spectral energy distributions with typical star-forming galaxy and IR-AGN templates. We then carefully removed the radio AGN candidates via a recursive approach. We find that the IRRC evolves primarily withM⋆, with more massive galaxies displaying a systematically lowerqIR. A secondary, weaker dependence on redshift is also observed. The best-fit analytical expression is the following:qIR(M⋆, z) = (2.646 ± 0.024) × (1 + z)( − 0.023 ± 0.008)–(0.148 ± 0.013) × (log M⋆/M⊙ − 10). Adding the UV dust-uncorrected contribution to the IR as a proxy for the total SFR would further steepen theqIRdependence onM⋆. We interpret the apparent redshift decline reported in previous works as due to low-M⋆galaxies being progressively under-represented at high redshift, as a consequence of binning only in redshift and using either infrared or radio-detected samples. The lower IR/radio ratios seen in more massive galaxies are well described by their higher observed SFR surface densities. Our findings highlight the fact that using radio-synchrotron emission as a proxy for SFR requires novelM⋆-dependent recipes that will enable us to convert detections from future ultra-deep radio surveys into accurate SFR measurements down to low-M⋆galaxies with low SFR.

SUPER

Feedback from active galactic nuclei (AGN) is thought to be key in shaping the life cycle of their host galaxies by regulating star-formation activity. Therefore, to understand the impact of AGN on star formation, it is essential to trace the molecular gas out of which stars form. In this paper we present the first systematic study of the CO properties of AGN hosts at z ≈ 2 for a sample of 27 X-ray selected AGN spanning two orders of magnitude in AGN bolometric luminosity (log Lbol / erg s−1 = 44.7 − 46.9) by using ALMA Band 3 observations of the CO(3-2) transition (∼1″ angular resolution). To search for evidence of AGN feedback on the CO properties of the host galaxies, we compared our AGN with a sample of inactive (i.e., non-AGN) galaxies from the PHIBSS survey with similar redshift, stellar masses, and star-formation rates (SFRs). We used the same CO transition as a consistent proxy for the gas mass for the two samples in order to avoid systematics involved when assuming conversion factors (e.g., excitation corrections and αCO). By adopting a Bayesian approach to take upper limits into account, we analyzed CO luminosities as a function of stellar masses and SFRs, as well as the ratio LCO(3–2)′/M∗ (a proxy for the gas fraction). The two samples show statistically consistent trends in the LCO(3–2)′−LFIR and LCO(3–2)′−M∗ planes. However, there are indications that AGN feature lower CO(3-2) luminosities (0.4–0.7 dex) than inactive galaxies at the 2–3σ level when we focus on the subset of parameters where the results are better constrained (i.e., LFIR ≈ 1012.2 L⊙ and M* > 1011 M⊙) and on the distribution of the mean log(LCO(3–2)′/M∗). Therefore, even by conservatively assuming the same excitation factor r31, we would find lower molecular gas masses in AGN, and assuming higher r31 would exacerbate this difference. We interpret our result as a hint of the potential effect of AGN activity (such as radiation and outflows), which may be able to heat, excite, dissociate, and/or deplete the gas reservoir of the host galaxies. Better SFR measurements and deeper CO observations for AGN as well as larger and more uniformly selected samples of both AGN and inactive galaxies are required to confirm whether there is a true difference between the two populations.

The next-generation X-ray galaxy survey with eROSITA

ABSTRACT eROSITA, launched on 2019 July 13, will be completing the first all-sky survey in the soft and medium X-ray band in nearly three decades. This 4-yr survey, finishing in late 2023, will present a rich legacy for the entire astrophysics community and complement upcoming multiwavelength surveys (with, e.g. the Large Synoptic Survey Telescope and the Dark Energy Survey). Besides the major scientific aim to study active galactic nuclei (AGNs) and galaxy clusters, eROSITAwill contribute significantly to X-ray studies of normal (i.e. not AGN) galaxies. Starting from multiwavelength catalogues, we measure star formation rates and stellar masses for 60 212 galaxies constrained to distances of 50–200 Mpc. We chose this distance range to focus on the relatively unexplored volume outside the local Universe, where galaxies will be largely spatially unresolved and probe a range of X-ray luminosities that overlap with the low luminosity and/or highly obscured AGN population. We use the most recent X-ray scaling relations as well as the on-orbit eROSITA instrument performance to predict the X-ray emission from XRBs and diffuse hot gas and to perform both an analytic prediction and an end-to-end simulation using the mission simulation software, sixte. We consider potential contributions from hidden AGN and comment on the impact of normal galaxies on the measurement of the faint end of the AGN luminosity function. We predict that the eROSITA 4-yr survey, will detect ≳15 000 galaxies (3σ significance) at 50–200 Mpc, which is ∼100 × more normal galaxies than detected in any X-ray survey to date.

An older, more quiescent universe from panchromatic SED fitting of the 3D-HST survey

AbstractGalaxies are complicated physical systems which obey complex scaling relationships; as a result, properties measured from broadband photometry are often highly correlated, degenerate, or both. Therefore, the accuracy of basic properties like stellar masses and star formation rates (SFRs) depend on the accuracy of many second-order galaxy properties, including star formation histories (SFHs), stellar metallicities, dust properties, and many others. Here, we re-assess measurements of galaxy stellar masses and SFRs using a 14-parameter physical model built in the Prospector Bayesian inference framework. We find that galaxies are ∼0.2 dex more massive and have ∼0.2 dex lower star formation rates than classic measurements. These measurements lower the observed cosmic star formation rate density and increase the observed buildup of stellar mass, finally bringing these two metrics into agreement at the factor-of-two level at 0.5 < z < 2.5.

Erratum: “A New Method to Measure Star Formation Rates in Active Galaxies Using Mid-infrared Neon Emission Lines” (2019, ApJ, 873, 103)

Erratum: “A New Method to Measure Star Formation Rates in Active Galaxies Using Mid-infrared Neon Emission Lines” (2019, ApJ, 873, 103)

A New Method to Measure Star Formation Rates in Active Galaxies Using Mid-infrared Neon Emission Lines

Abstract The star formation rate (SFR) is one of the most fundamental parameters of galaxies, but nearly all of the standard SFR diagnostics are difficult to measure in active galaxies because of contamination from the active galactic nucleus (AGN). Being less sensitive to dust extinction, the mid-infrared fine-structure lines of [Ne ii] 12.81 μm and [Ne iii] 15.56 μm effectively trace the SFR in star-forming galaxies. These lines also have the potential to serve as a reliable SFR indicator in active galaxies, provided that their contribution from the AGN narrow-line region (NLR) can be removed. We use a new set of photoionization calculations with realistic AGN spectral energy distributions and input assumptions to constrain the magnitude of [Ne ii] and [Ne iii] produced by the NLR for a given strength of [Ne v] 14.32 μm. We demonstrate that AGNs emit a relatively restricted range of [Ne ii]/[Ne v] and [Ne iii]/[Ne v] ratios. Hence, once [Ne v] is measured,the AGN contribution to the low-ionization Ne lines can be estimated, and the SFR can be determined from the strength of [Ne ii] and [Ne iii]. We find that AGN host galaxies have similar properties as compact extragalactic H ii regions, which indicates that the star formation in AGN hosts is spatially concentrated. This suggests a close relationship between black hole accretion and nuclear star formation. We update the calibration of [Ne ii] and [Ne iii] strength as an SFR indicator, explicitly considering the effects of metallicity, finding very good relations between Ne fractional abundances and the [Ne iii]/[Ne ii] ratio for different metallicities, ionization parameters, and starburst ages. Comparison of neon-based SFRs with independent SFRs for active and star-forming galaxies shows excellent consistency with small scatter (∼0.18 dex).

Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR

Context. Radio continuum (RC) emission in galaxies allows us to measure star formation rates (SFRs) unaffected by extinction due to dust, of which the low-frequency part is uncontaminated from thermal (free–free) emission. Aims. We calibrate the conversion from the spatially resolved 140 MHz RC emission to the SFR surface density (ΣSFR) at 1 kpc scale. Radio spectral indices give us, by means of spectral ageing, a handle on the transport of cosmic rays using the electrons as a proxy for GeV nuclei. Methods. We used recent observations of three galaxies (NGC 3184, 4736, and 5055) from the LOFAR Two-metre Sky Survey (LoTSS), and archival LOw-Frequency ARray (LOFAR) data of NGC 5194. Maps were created with the facet calibration technique and converted to radio ΣSFR maps using the Condon relation. We compared these maps with hybrid ΣSFR maps from a combination of GALEX far-ultraviolet and Spitzer 24 μm data using plots tracing the relation at the highest angular resolution allowed by our data at 1.2 × 1.2 kpc2 resolution. Results. The RC emission is smoothed with respect to the hybrid ΣSFR owing to the transport of cosmic-ray electrons (CREs) away from star formation sites. This results in a sublinear relation (ΣSFR)RC ∝ [(ΣSFR)hyb]a, where a = 0.59 ± 0.13 (140 MHz) and a = 0.75 ± 0.10 (1365 MHz). Both relations have a scatter of σ = 0.3 dex. If we restrict ourselves to areas of young CREs (α > −0.65; Iν ∝ να), the relation becomes almost linear at both frequencies with a ≈ 0.9 and a reduced scatter of σ = 0.2 dex. We then simulate the effect of CRE transport by convolving the hybrid ΣSFR maps with a Gaussian kernel until the RC–SFR relation is linearised; CRE transport lengths are l = 1–5 kpc. Solving the CRE diffusion equation, assuming dominance of the synchrotron and inverse-Compton losses, we find diffusion coefficients of D = (0.13–1.5) × 1028 cm2 s−1 at 1 GeV. Conclusions. A RC–SFR relation at 1.4 GHz can be exploited to measure SFRs at redshift z ≈ 10 using 140 MHz observations.

Slow-then-rapid quenching as traced by tentative evidence for enhanced metallicities of cluster galaxies at z ∼ 0.2 in the slow quenching phase

Aims. As large-scale structures in the Universe develop with time, environmental effects become more and more important as a star formation quenching mechanism. Since the effects of environmental quenching are more pronounced in denser structures that form at later times, we seek to constrain environmental quenching processes using cluster galaxies at z < 0.3. Methods. We explored seven clusters from the Local Cluster Substructure Survey (LoCuSS) at 0.15 < z < 0.26 with spectra of 1965 cluster members in a mass-complete sample from the ACReS (Arizona Cluster Redshift Survey) Hectospec survey covering a region that corresponds to about three virial radii for each cluster. We measured fluxes of [O II] λ 3727, Hβ, [O III] λ 5007, Hα, and [N II] λ 6584 emission lines of cluster members, enabling us to unambiguously derive O/H gas metallicities. We also measured star formation rates (SFRs) from extinction-corrected Hα fluxes. We compared our cluster galaxy sample with a field sample of 705 galaxies at similar redshifts observed with Hectospec as part of the same survey. Results. We find that star-forming cluster and field galaxies show similar median specific SFRs in a given mass bin of 1 − 3.2 × 1010 M⊙ and 3.2 − 10 × 1010 M⊙, respectively. But their O/H values are displaced, in the lower mass bin, to higher values (significance 2.4σ) at projected radii of R < R200 compared with galaxies at larger radii and in the field. The comparison with metallicity-SFR-mass model predictions with inflowing gas indicates a slow-quenching scenario in which strangulation is initiated when galaxies pass R ∼ R200 by stopping the inflow of gas. We find tentative evidence that the metallicities of cluster members inside R200 are thereby increasing, but their SFRs are hardly affected for a period of time because these galaxies consume available disk gas. We use the observed fraction of star-forming cluster galaxies as a function of clustercentric radius compared to predictions from the Millennium simulation to constrain quenching timescales to be 1−2 Gyr, which is defined as the time between the moment the galaxy passes R200 until complete quenching of star formation. This is consistent with a slow-then-rapid quenching scenario. Slow quenching (strangulation) starts when the gas inflow is stopped when the galaxy passes R200 with a phase in which cluster galaxies are still star forming, but they show elevated metallicities tracing the ongoing quenching. This phase lasts for 1−2 Gyr, and meanwhile the galaxies travel to denser inner regions of the cluster. This is followed by a “rapid” phase, i.e., a rapid complete quenching of star formation due to the increasing ram pressure toward the cluster center that can also strip the cold gas in massive galaxies.

Galaxy Inclination and the IRX–β Relation: Effects on UV Star Formation Rate Measurements at Intermediate to High Redshifts

Abstract At intermediate and high redshifts, measurements of galaxy star formation rates are usually based on rest-frame ultraviolet (UV) data. A correction for dust attenuation, A UV, is needed for these measurements. This correction is typically inferred from UV spectral slopes (β) using an equation known as “Meurer’s Relation.” In this paper, we study this relation at a redshift of 1.5 using images and photometric measurements in the rest-frame UV (HST) through mid-infrared (Spitzer). It is shown that massive star-forming galaxies (above ) have dust corrections that are dependent on their inclination to the line of sight. Edge-on galaxies have higher A UV and infrared excess (IRX = L(IR)/L(UV)) than face-on galaxies at a given β. Interestingly, dust corrections for low-mass star-forming galaxies do not depend on inclination. This is likely because more massive galaxies have more disk-like shapes/kinematics, while low-mass galaxies are more prolate and have more disturbed kinematics. To account for an inclination-dependent dust correction, a modified Meurer’s Relation is derived: , where b/a is the galaxy axis ratio. This inclination dependence of A UV can be explained by a two-component model of the dust distribution inside galaxies. In such a model, the dust attenuation of edge-on galaxies has a higher contribution from a mixture component (dust uniformly mixed with stars in the diffuse interstellar medium), and a lower contribution from a birth cloud component (near-spherical dust shells surrounding young stars in H ii regions) than that of face-on galaxies. The difference is caused by the larger path lengths through disks at higher inclinations.

The Star Formation Reference Survey – III. A multiwavelength view of star formation in nearby galaxies

We present multi-wavelength global star formation rate (SFR) estimates for 326 galaxies from the Star Formation Reference Survey (SFRS) in order to determine the mutual scatter and range of validity of different indicators. The widely used empirical SFR recipes based on 1.4 GHz continuum, 8.0 $\mu$m polycyclic aromatic hydrocarbons (PAH), and a combination of far-infrared (FIR) plus ultraviolet (UV) emission are mutually consistent with scatter of $\raise{-0.8ex}\stackrel{\textstyle <}{\sim }$0.3 dex. The scatter is even smaller, $\raise{-0.8ex}\stackrel{\textstyle <}{\sim }$0.24 dex, in the intermediate luminosity range 9.3<log(L(60 $\mu$m/L$_\odot$)<10.7. The data prefer a non-linear relation between 1.4 GHz luminosity and other SFR measures. PAH luminosity underestimates SFR for galaxies with strong UV emission. A bolometric extinction correction to far-ultraviolet luminosity yields SFR within 0.2 dex of the total SFR estimate, but extinction corrections based on UV spectral slope or nuclear Balmer decrement give SFRs that may differ from the total SFR by up to 2 dex. However, for the minority of galaxies with UV luminosity ${>}5\times10^9$ L$_{\odot}$ or with implied far-UV extinction <1 mag, the UV spectral slope gives extinction corrections with 0.22~dex uncertainty.

The star formation law at GMC scales in M33, the Triangulum galaxy

We present a high spatial resolution study, on scales of $\sim$100pc, of the relationship between star-formation rate (SFR) and gas content within Local Group galaxy M33. Combining deep SCUBA-2 observations with archival GALEX, SDSS, WISE, Spitzer and submillimetre Herschel data, we are able to model the entire SED from UV to sub-mm wavelengths. We calculate the SFR on a pixel-by-pixel basis using the total infrared luminosity, and find a total SFR of $0.17 \pm 0.06\,\rm{M}_\odot$/yr, somewhat lower than our other two measures of SFR -- combined FUV and 24$\mu$m SFR ($0.25^{+0.10}_{-0.07}\,\rm{M}_\odot$/yr) and SED-fitting tool MAGPHYS ($0.33^{+0.05}_{-0.06}\,\rm{M}_\odot$/yr). We trace the total gas using a combination of the 21cm HI line for atomic hydrogen, and CO($\textit{J}$=2-1) data for molecular hydrogen. We have also traced the total gas using dust masses. We study the star-formation law in terms of molecular gas, total gas, and gas from dust. We perform an analysis of the star-formation law on a variety of pixel scales, from 25$^{\prime\prime}$ to 500$^{\prime\prime}$ (100pc to 2kpc). At kpc scales, we find that a linear Schmidt-type power law index is suitable for molecular gas, but the index appears to be much higher with total gas, and gas from dust. Whilst we find a strong scale dependence on the Schmidt index, the gas depletion timescale is invariant with pixel scale.