Instantaneous Star Formation Rate Research Articles

Pulling Back the Curtain on Shocks and Star Formation in NGC 1266 with Gemini-NIFS

We present Gemini near-infrared integral field spectrograph K-band observations of the central 400 pc of NGC 1266, a nearby (D ≈ 30 Mpc) post-starburst galaxy with a powerful multiphase outflow and a shocked interstellar medium. We detect seven H2 rovibrational emission lines excited thermally to T ∼ 2000 K, and weak Brγ emission, consistent with a fast continuous shock (or C-shock). With these bright H2 lines, we observe the spatial structure of the shock with an unambiguous tracer for the first time. The Brγ emission is concentrated in the central ≲100 pc, indicating that any remaining star formation in NGC 1266 is in the nucleus, while the surrounding cold molecular gas has little ongoing star formation. Though it is unclear what fraction of this Brγ emission is from star formation or the active galactic nuclei (AGN), assuming it is entirely due to star formation we measure an instantaneous star formation rate of 0.7 M ⊙ yr−1, though the star formation rate may be significantly higher in the presence of additional extinction. NGC 1266 provides a unique laboratory to study the complex interactions between AGN, outflows, shocks, and star formation, all of which are necessary to unravel the evolution of the post-starburst phase.

Measuring 60 pc-scale Star Formation Rate of the Nearby Seyfert Galaxy NGC 1068 with ALMA, HST, VLT/MUSE, and VLA

The star formation rate (SFR) is a fundamental parameter for describing galaxies and inferring their evolutionary course. H ii regions yield the best measure of instantaneous SFR in galaxies, although the derived SFR can have large uncertainties depending on tracers and assumptions. We present an SFR calibration for the entire molecular gas disk of the nearby Seyfert galaxy NGC 1068, based on our new high-sensitivity Atacama Large Millimeter/submillimeter Array 100 GHz continuum data at 55 pc (= 0.″8) resolution in combination with the Hubble Space Telescope Paα line data. In this calibration, we account for the spatial variations of dust extinction, electron temperature of H ii regions, AGN contamination, and diffuse ionized gas (DIG) based on publicly available multiwavelength data. Especially, given the extended nature and the possible nonnegligible contribution to the total SFR, a careful consideration of DIG is essential. With a cross-calibration between two corrected ionized gas tracers (free–free continuum and Paα), the total SFR of the NGC 1068 disk is estimated to be 3.2 ± 0.5 M ⊙ yr−1, one-third of the SFR without accounting for DIG (9.1 ± 1.4 M ⊙ yr−1). We confirmed a high SFR around the southern bar end and the corotation radius, which is consistent with the previous SFR measurements. In addition, our total SFR exceeds the total SFR based on 8 μm dust emission by a factor of 1.5. We attribute this discrepancy to the differences in the young stars at different stages of evolution traced by each tracer and their respective timescales. This study provides an example to address the various uncertainties in conventional SFR measurements and their potential to lead to significant SFR miscalculations.

Spatially resolved Hα and ionizing photon production efficiency in the lensed galaxy MACS1149-JD1 at a redshift of 9.11

We present MIRI/JWST medium-resolution spectroscopy (MRS) and imaging (MIRIM) of the lensed galaxy MACS1149-JD1 at a redshift of z = 9.1092 ± 0.0002, when the Universe was about 530 Myr old. We detect, for the first time, spatially resolved Hα emission in a galaxy at a redshift above nine. The structure of the Hα emitting gas consists of two clumps, S and N, carrying about 60% and 40% of the total flux, respectively. The total Hα luminosity implies an instantaneous star-formation rate in the range of 3.2 ± 0.3 and 5.3 ± 0.4 M⊙ yr−1 for sub-solar and solar metallicities. The ionizing photon production efficiency, log(ζion), shows a spatially resolved structure with values of 25.55 ± 0.03; 25.47 ± 0.03; and 25.91 ± 0.09 Hz erg−1 for the integrated galaxy and clumps S and N, respectively. The Hα rest-frame equivalent width, EW0 (Hα), is 726−182+660 Å for the integrated galaxy, but it presents extreme values of 531−96+300 Å and ≥1951 Å for clumps S and N, respectively. The spatially resolved ionizing photon production efficiency is within the range of values measured in galaxies at a redshift above six and well above the canonical value (25.2 ± 0.1 Hz erg−1). The EW0 (Hα) is a factor of two lower than the predicted value at z = 9.11 based on the extrapolation of the evolution of the EW0 (Hα) with redshifts, ∝(1 + z)2.1, including galaxies detected with JWST. The extreme difference of the EW0 (Hα) for clumps S and N indicates the presence of a recent (< 5 Myr) stellar burst in clump N and a star formation over a larger period of time (e.g., ∼50 Myr) in clump S. The different ages of the stellar population place MACS1149-JD1 and clumps N and S at different locations in the log(ζion) to EW0 (Hα) plane and above the main relation defined from intermediate- and high-redshift (z = 3 − 7) galaxies detected with JWST. Finally, clump S and N show very different Hα kinematics, with velocity dispersions of 56 ± 4 km s−1 and 113 ± 33 km s−1, likely indicating the presence of outflows or increased turbulence in clump N. The dynamical mass Mdyn = (2.4 ± 0.5) × 109 M⊙, obtained from the size of the integrated Hα ionized nebulae and its velocity dispersion, is within the range previously measured with the spatially resolved [OIII]88 μm line.

Dust- and inclination-corrected star formation and interstellar medium scaling relations in nearby galaxies

ABSTRACT Following from our recent work, we present a detailed analysis of star formation and interstellar medium (ISM) scaling relations, done on a representative sample of nearby galaxies. H α images are analysed in order to derive the integrated galaxy luminosity, known as a more instantaneous and accurate star formation rate (SFR) tracer, and the required photometric and structural parameters. Dust- and inclination-corrected H α luminosities, SFRs, and related quantities are determined using a self-consistent method based on previous work prescriptions, which does not require the assumption of a dust attenuation curve and use of Balmer decrements (or other hydrogen recombination lines) to estimate the dust attenuation, with the advantage of determining dust opacities and dust masses along the way. We investigate the extent to which the dust and inclination effects bias the specific parameters of these relations, the scatter and degree of correlation, and which relations are fundamental or are just a consequence of others. Most of our results are consistent with errors with other similar studies, while others come in opposition or are inconclusive. By comparing the B-band optical and H α (star-forming) discs scale lengths, we found on average the star formation distribution to be more extended than the stellar continuum emission one (the ratio being 1.10), this difference increasing with stellar mass. Similarly, more massive galaxies have a more compact stellar emission surface density than the star formation one (average ratio of 0.77). The method proposed can be applied in larger scale studies of star formation and ISM evolution, for normal low- to intermediate-redshift galaxies.

Mangrove: Learning Galaxy Properties from Merger Trees

Efficiently mapping baryonic properties onto dark matter is a major challenge in astrophysics. Although semianalytic models (SAMs) and hydrodynamical simulations have made impressive advances in reproducing galaxy observables across cosmologically significant volumes, these methods still require significant computation times, representing a barrier to many applications. Graph neural networks have recently proven to be the natural choice for learning physical relations. Among the most inherently graph-like structures found in astrophysics are the dark matter merger trees that encode the evolution of dark matter halos. In this paper, we introduce a new, graph-based emulator framework, Mangrove, and show that it emulates the galactic stellar mass, cold gas mass and metallicity, instantaneous and time-averaged star formation rate, and black hole mass—as predicted by an SAM—with an rms error up to 2 times lower than other methods across a (75 Mpc/h)3 simulation box in 40 s, 4 orders of magnitude faster than the SAM. We show that Mangrove allows for quantification of the dependence of galaxy properties on merger history. We compare our results to the current state of the art in the field and show significant improvements for all target properties. Mangrove is publicly available: https://github.com/astrockragh/Mangrove.

Early Results from GLASS-JWST. IV. Spatially Resolved Metallicity in a Low-mass z ∼ 3 Galaxy with NIRISS* *Based on observations acquired by the JWST under the ERS program ID 1324 (PI T. Treu).

We report the first gas-phase metallicity map of a distant galaxy measured with the James Webb Space Telescope (JWST). We use the NIRISS slitless spectroscopy acquired by the GLASS Early Release Science program to spatially resolve the rest-frame optical nebular emission lines in a gravitationally lensed galaxy at z = 3.06 behind the A2744 galaxy cluster. This galaxy (dubbed GLASS-Zgrad1) has stellar mass ∼108.6 M ⊙, instantaneous star formation rate ∼8.6 M ⊙ yr−1 (both corrected for lensing magnification), and global metallicity one-fourth solar. From its emission-line maps ([O iii], Hβ, Hγ, [Ne iii], and [O ii]), we derive its spatial distribution of gas-phase metallicity using a well-established forward-modeling Bayesian inference method. The exquisite resolution and sensitivity of JWST/NIRISS, combined with lensing magnification, enable us to resolve this z ∼ 3 dwarf galaxy in ≳50 resolution elements with sufficient signal, an analysis hitherto not possible. We find that the radial metallicity gradient of GLASS-Zgrad1 is strongly inverted (i.e., positive): = 0.165 ± 0.023 dex kpc−1. This measurement is robust at confidence level against known systematics. This positive gradient may be due to tidal torques induced by a massive nearby (∼15 kpc projected) galaxy, which can cause inflows of metal-poor gas into the central regions of GLASS-Zgrad1. These first results showcase the power of JWST wide-field slitless spectroscopic modes to resolve the mass assembly and chemical enrichment of low-mass galaxies in and beyond the peak epoch of cosmic star formation (z ≳ 2). Reaching masses ≲ 109 M ⊙ at these redshifts is especially valuable to constrain the effects of galactic feedback and environment and is possible only with JWST’s new capabilities.

On the Connection between Supermassive Black Holes and Galaxy Growth in the Reionization Epoch

The correlation between the mass of supermassive black holes (SMBHs; ) and their host galaxies () in the reionization epoch provides valuable constraints on their early growth. High-redshift quasars typically have an / ratio significantly elevated in comparison to the local value. However, the degree to which this apparent offset is driven by observational biases is unclear for the most distant quasars. To address this issue, we model the sample selection and measurement biases for a compilation of 20 quasars at z ∼ 6 with host properties based on ALMA observations. We find that the observed distribution of quasars in the plane can be reproduced by assuming that the underlying SMBH population at z ∼ 6 follows the relationship in the local universe. However, a positive or even a negative evolution in / can also explain the data, depending on whether the intrinsic scatter evolves and on the strength of various systematic uncertainties. To break these degeneracies, an improvement in the accuracy of mass measurements and an expansion of the current sample to lower limits are needed. Furthermore, assuming a radiative efficiency of 0.1 and quasar duty cycles estimated from the active SMBH fraction, significant outliers in / tend to move toward the local relation given their instantaneous BH growth rate and star formation rate. This may provide evidence for a self-regulated SMBH–galaxy coevolution scenario that is in place at z ∼ 6, with active galactic nucleus feedback being a possible driver.

The Mass–Metallicity Relation at Cosmic Noon in Overdense Environments: First Results from the MAMMOTH–Grism HST Slitless Spectroscopic Survey

Abstract The MAMMOTH–Grism slitless spectroscopic survey is a Hubble Space Telescope (HST) cycle 28 medium program, which is obtaining 45 orbits of WFC3/IR grism spectroscopy in the density peak regions of three massive galaxy protoclusters at z = 2–3 discovered using the MAMMOTH technique. We introduce this survey by presenting the first measurement of the mass–metallicity relation (MZR) at high redshift in overdense environments via grism spectroscopy. From the completed MAMMOTH–Grism observations in the field of the BOSS1244 protocluster at z = 2.24 ± 0.02, we secure a sample of 36 protocluster member galaxies at z ≈ 2.24, showing strong nebular emission lines ([O III], Hβ, and [O II]) in their G141 spectra. Using the multi-wavelength broadband deep imaging from HST and ground-based telescopes, we measure their stellar masses in the range of [109, 1010.4] M ⊙, instantaneous star formation rates (SFR) from 10 to 240 M ⊙ yr−1, and global gas-phase metallicities [ 1 3 , 1 ] of solar. Compared with similarly selected field-galaxy samples at the same redshift, our galaxies show, on average, increased SFRs by ∼0.06 dex and ∼0.18 dex at ∼1010.1 M ⊙ and ∼109.8 M ⊙, respectively. Using the stacked spectra of our sample galaxies, we derive the MZR in the BOSS1244 protocluster core as 12 + log ( O / H ) = 0.136 ± 0.018 × log ( M * / M ⊙ ) + 7.082 ± 0.175 , showing a significantly shallower slope than that in the field. This shallow MZR slope is likely caused by the combined effects of efficient recycling of feedback-driven winds and cold-mode gas accretion in protocluster environments. The former effect helps low-mass galaxies residing in overdensities retain their metal production, whereas the latter effect dilutes the metal content of high-mass galaxies, making them more metal-poor than their coeval field counterparts.

The Stellar Mass versus Stellar Metallicity Relation of Star-forming Galaxies at 1.6 ≤ z ≤ 3.0 and Implications for the Evolution of the α-enhancement

Abstract We measure the relationship between stellar mass and stellar metallicity for 1336 star-forming galaxies at 1.6 ≤ z ≤ 3.0 using rest-frame far-ultraviolet spectra from the zCOSMOS-deep survey. High signal-to-noise ratio composite spectra containing stellar absorption features are fit with stellar population synthesis model spectra of a range of stellar metallicity. We find stellar metallicities, which mostly reflect instantaneous iron abundances, scaling as [ Fe / H ] = − ( 0.81 ± 0.01 ) + ( 0.32 + 0.03 ) log ( M * / 10 10 M ⊙ ) across the stellar mass range of 109 ≲ M */M ⊙ ≲ 1011. The instantaneous oxygen-to-iron ratio (α-enhancement) inferred using the gas-phase mass–metallicity relation is on average found to be O / Fe ≈ 0.47 , being higher than the local O / Fe ≈ 0 . The observed changes in [O/Fe] and [Fe/H] are reproduced in simple gas-regulator models with steady star formation histories. Our models show that the [O/Fe] is determined almost entirely by the instantaneous specific star formation rate alone while being independent of the mass and the characteristic of the gas regulation. We also find that the locations of ∼ 1010 M ⊙ galaxies at z ∼ 2 in the [O/Fe]–metallicity planes are in remarkable agreement with the sequence of low-metallicity thick-disk stars in our own Galaxy. This manifests a beautiful concordance between the results of Galactic archeology and observations of high-redshift Milky Way progenitors. There remains, however, a question of how and when the old metal-rich, low α/Fe stars seen in the bulge had formed by z ∼ 2 because such a stellar population is not seen in our data and is difficult to explain in the context of our models.

Observing correlations between dark matter accretion and galaxy growth: II. testing the impact of galaxy mass, star formation indicator, and neighbour colours

ABSTRACT A crucial question in galaxy formation is what role new accretion has in star formation. Theoretical models have predicted a wide range of correlation strengths between halo accretion and galaxy star formation. Previously, we presented a technique to observationally constrain this correlation strength for isolated Milky Way mass galaxies at z ∼ 0.12, based on the correlation between halo accretion and the density profile of neighbouring galaxies. By applying this technique to both observational data from the Sloan Digital Sky Survey and simulation data from the UniverseMachine, where we can test different correlation strengths, we ruled out positive correlations between dark matter accretion and recent star formation activity. In this work, we expand our analysis by (1) applying our technique separately to red and blue neighbouring galaxies, which trace different infall populations, (2) correlating dark matter accretion rates with Dn 4000 measurements as a longer-term quiescence indicator than instantaneous star-formation rates, and (3) analysing higher-mass isolated central galaxies with 1011.0 < M*/M⊙ < 1011.5 out to z ∼ 0.18. In all cases, our results are consistent with non-positive correlation strengths with ≳ 85 per cent confidence, which is most consistent with models where processes such as gas recycling dominate star formation in massive z = 0 galaxies.

NOEMA Redshift Measurements of Extremely Bright Submillimeter Galaxies near the GOODS-N

Abstract We report spectroscopic redshift measurements for three bright submillimeter galaxies (SMGs) near the GOODS-N field, each with SCUBA-2 850 μm fluxes >10 mJy, using the Northern Extended Millimeter Array (NOEMA). Our molecular line-scan observations of these sources, which occupy an ∼7 arcmin2 area outside of the Hubble Space Telescope coverage of the field, reveal that two lie at z ∼ 3.14. In the remaining object, we detect line emission consistent with CO(7–6), [C i], and H2O at z = 4.42. The far-infrared spectral energy distributions of these galaxies, constrained by SCUBA-2, NOEMA, and Herschel/SPIRE, indicate instantaneous star formation rates ∼4000 M ⊙ yr−1 in the z = 4.42 galaxy and ∼2500 M ⊙ yr−1 in the two z ∼ 3.14 galaxies. Based on the sources’ CO line luminosities, we estimate M gas ∼ 1011 M ⊙ and find gas depletion timescales of τ depl ∼ 50 Myr, consistent with findings in other high-redshift SMGs. Finally, we show that the two z ∼ 3.14 sources, which alone occupy a volume ∼10 Mpc3, very likely mark the location of a protocluster of bright SMGs and less-dusty optical sources.

H i-MaNGA: tracing the physics of the neutral and ionized ISM with the second data release

ABSTRACT We present the second data release for the H i-MaNGA programme of H i follow-up observations for the SDSS-IV MaNGA survey. This release contains measurements for 3669 unique galaxies, combining 2108 Green Bank Telescope observations with an updated crossmatch of the MaNGA sample with the ALFALFA survey. We combine these data with MaNGA spectroscopic measurements to examine relationships between H i-to-stellar mass ratio (${\rm M_{H\, {\small I}}/{M_*}}$) and average ISM/star formation properties probed by optical emission lines. ${\rm M_{H\, {\small I}}/{M_*}}$ is very weakly correlated with the equivalent width of H α, implying a loose connection between the instantaneous star formation rate and the H i reservoir, although the link between ${\rm M_{H\, {\small I}}/{M_*}}$ and star formation strengthens when averaged even over only moderate time-scales (∼30 Myr). Galaxies with elevated H i depletion times have enhanced [O i]/H α and depressed H α surface brightness, consistent with more H i residing in a diffuse and/or shock-heated phase that is less capable of condensing into molecular clouds. Of all optical lines, ${\rm M_{H\, {\small I}}/{M_*}}$ correlates most strongly with oxygen equivalent width, EW(O), which is likely a result of the existing correlation between ${\rm M_{H\, {\small I}}/{M_*}}$ and gas-phase metallicity. Residuals in the ${\rm M_{H\, {\small I}}/{M_*}}$−EW(O) relation are again correlated with [O i]/H α and H α surface brightness, suggesting they are also driven by variations in the fraction of diffuse and/or shock-heated gas. We recover the strong anticorrelation between ${\rm M_{H\, {\small I}}/{M_*}}$ and gas-phase metallicity seen in previous studies. We also find a relationship between ${\rm M_{H\, {\small I}}/{M_*}}$ and [O i]6302/H α, suggesting that higher fractions of diffuse and/or shock-heated gas are more prevalent in gas-rich galaxies.

A Census of Sub-kiloparsec Resolution Metallicity Gradients in Star-forming Galaxies at Cosmic Noon from HST Slitless Spectroscopy

Abstract We present the hitherto largest sample of gas-phase metallicity radial gradients measured at sub-kpc resolution in star-forming galaxies in the redshift range of z ∈ [1.2, 2.3]. These measurements are enabled by the synergy of slitless spectroscopy from the Hubble Space Telescope near-infrared channels and the lensing magnification from foreground galaxy clusters. Our sample consists of 76 galaxies with stellar mass ranging from 107 to 1010 , an instantaneous star formation rate in the range of [1, 100] yr−1, and global metallicity of solar. At a 2σ confidence level, 15/76 galaxies in our sample show negative radial gradients, whereas 7/76 show inverted gradients. Combining ours and all other metallicity gradients obtained at a similar resolution currently available in the literature, we measure a negative mass dependence of Δlog(O/H)/ = (−0.020 ± 0.007) + (−0.016 ± 0.008) , with the intrinsic scatter being σ = 0.060 ± 0.006 over 4 orders of magnitude in stellar mass. Our result is consistent with strong feedback, not secular processes, being the primary governor of the chemostructural evolution of star-forming galaxies during the disk mass assembly at cosmic noon. We also find that the intrinsic scatter of metallicity gradients increases with decreasing stellar mass and increasing specific star formation rate. This increase in the intrinsic scatter is likely caused by the combined effect of cold-mode gas accretion and merger-induced starbursts, with the latter more predominant in the dwarf mass regime of .

The impact of starbursts on element abundance ratios

ABSTRACT We investigate the impact of bursts in star formation on the predictions of one-zone chemical evolution models, adopting oxygen (O), iron (Fe), and strontium (Sr), as representative α, iron-peak, and s-process elements, respectively. To this end, we develop and make use of the Versatile Integrator for Chemical Evolution (VICE), a python package designed to handle flexible user-specified evolutionary parameters. Starbursts driven by a temporary boost of gas accretion rate create loops in [O/Fe]–[Fe/H] evolutionary tracks and a peak in the stellar [O/Fe] distribution at intermediate values. Bursts driven by a temporary boost of star formation efficiency have similar effects, and they also produce a population of α-deficient stars during the depressed star formation phase following the burst. This α-deficient population is more prominent if the outflow rate is tied to a time-averaged star formation rate (SFR) instead of the instantaneous SFR. Theoretical models of Sr production predict a strong metallicity dependence of supernova and asymptotic giant branch star yields, though comparison to data suggests an additional, nearly metallicity-independent source. Evolution of [Sr/Fe] and [Sr/O] during a starburst is complex because of this metallicity dependence and the multiple time-scales at play. Moderate amplitude (10–20 per cent) sinusoidal oscillations in SFR produce loops in [O/Fe]–[Fe/H] tracks and multiple peaks in [O/Fe] distributions, a potential source of intrinsic scatter in observed sequences. We investigate the impact of a factor ∼2 enhancement of Galactic star formation ∼2 Gyr ago, as suggested by some recent observations. VICE is publicly available at <http://pypi.org/project/vice/>.

O ii] emitters in MultiDark-Galaxies and DEEP2

ABSTRACT We use three semi-analytical models (SAMs) of galaxy formation and evolution run on the same 1 h−1 Gpc MultiDark Planck2 cosmological simulation to investigate the properties of [O ii] emission line galaxies at redshift z ∼ 1. We compare model predictions with different observational data sets, including DEEP2–firefly galaxies with absolute magnitudes. We estimate the [O ii] luminosity ($L{\left[\rm{O\,{\small II}}\right]}$) of our model galaxies using the public code get_ emlines , which ideally assumes as input the instantaneous star formation rates (SFRs). This property is only available in one of the SAMs under consideration, while the others provide average SFRs, as most models do. We study the feasibility of inferring galaxies’ $L{\left[\rm{O\,{\small II}}\right]}$ from average SFRs in post-processing. We find that the result is accurate for model galaxies with dust attenuated $L{\left[\rm{O\,{\small II}}\right]}$ ≲ 1042.2 erg s−1 ($\lt 5{{\ \rm per\ cent}}$ discrepancy). The galaxy properties that correlate the most with the model $L{\left[\rm{O\,{\small II}}\right]}$ are the SFR and the observed-frame u and g broad-band magnitudes. Such correlations have r-values above 0.64 and a dispersion that varies with $L{\left[\rm{O\,{\small II}}\right]}$ . We fit these correlations with simple linear relations and use them as proxies for $L{\left[\rm{O\,{\small II}}\right]}$ , together with an observational conversion that depends on SFR and metallicity. These proxies result in [O ii] luminosity functions and halo occupation distributions with shapes that vary depending on both the model and the method used to derive $L{\left[\rm{O\,{\small II}}\right]}$ . The amplitude of the clustering of model galaxies with $L{\left[\rm{O\,{\small II}}\right]}$ >1040.4 erg s−1 remains overall unchanged on scales above 1 $\, h^{-1}$ Mpc, independently of the $L{\left[\rm{O\,{\small II}}\right]}$ computation.

Chemical enrichment and host galaxies of extremely strong intervening DLAs towards quasars

We present the results from VLT/X-shooter spectroscopic observations of 11 extremely strong intervening damped Lyman-α absorbers (ESDLAs) that were initially selected as high N(H I) (i.e. ≥5 × 1021 cm−2) candidates from the Sloan Digital Sky Survey (SDSS). We confirm the high H I column densities, which we measure to be in the range log N(H I) = 21.6 − 22.4. Molecular hydrogen is detected with high column densities (N(H2)≥1018 cm−2) in 5 out of 11 systems, 3 of which are reported here for the first time, and we obtain conservative upper limits on N(H2) for the remaining 6 systems. We also measure the column density of various metal species (Zn II, Fe II, Si II, Cr II, and C I), quantify the absorption-line kinematics (Δv90), and estimate the extinction of the background quasar light (AV) by dust in the absorbing gas. We compare the chemical properties of this sample of ESDLAs, supplemented with literature measurements, to that of DLAs located at the redshift of long-duration γ-ray bursts (GRB-DLAs). We confirm that the two populations are almost indistinguishable in terms of chemical enrichment and gas kinematics. In addition, we find no marked differences in the incidence of H2. All this suggests that ESDLAs and GRB-DLAs probe similar galactic environments. We search for the galaxy counterparts of ESDLAs and find associated emission lines in 3 out of 11 systems, 2 of which are reported here for the first time (at zabs = 2.304 and 2.323 towards the quasars SDSS J002503.03+114547.80 and SDSS J114347.21+142021.60, respectively). The measured separations between the quasar sightlines and the emission associated with the ESDLA galaxy (for a total of five sightlines) are all very small (ρ < 3 kpc). Because our observations are complete up to ρ ∼ 7 kpc, we argue that the emission counterparts of the remaining systems are more likely below the detection limit than outside the search area. While the small impact parameters are similar to what is observed for GRB-DLAs, the associated star formation rates are on average lower than for GRB host galaxies. This is explained by long-duration GRBs being associated with the death of massive stars and therefore pinpointing regions of active star formation in the GRB host galaxies. Our observations support the suggestion from the literature that ESDLAs could act as blind analogues of GRB-DLAs, probing neutral gas with high column density in the heart of high-redshift galaxies, without any prior on the instantaneous star formation rate.

Bright Lyman-α emitters among Spitzer SMUVS galaxies in the MUSE/COSMOS field

We search for the presence of bright Lyα emitters among Spitzer SMUVS galaxies at z > 2.9 making use of homogeneous MUSE spectroscopic data. Although these data only cover a small region of COSMOS, MUSE has the unique advantage of providing spectral information over the entire field, without the need of target pre-selection. This results in an unbiased detection of all the brightest Lyα emitters among the SMUVS sources, which by design are stellar-mass selected galaxies. Within the studied area, ∼14% of the SMUVS galaxies at z > 2.9 have Lyα fluxes Fλ ≳ 7 × 10−18 erg s−1 cm−2. These Lyα emitters are characterized by three types of emission, 47% show a single-line profile, 19% present a double peak or a blue bump, and 31% show a red tail. One object (3%) shows both a blue bump and a red tail. We also investigate the spectral energy distribution (SED) properties of the SMUVS galaxies that are MUSE detected and those that are not. After stellar mass matching the two populations, we find that the MUSE detected galaxies have generally lower extinction than SMUVS-only objects, while there is no clear intrinsic difference in the mass and age distributions of the two samples. For the MUSE-detected SMUVS galaxies, we compare the instantaneous star formation rate lower limit obtained from the Lyα line with its past average derived from SED fitting, and find evidence for rejuvenation in some of our oldest objects. In addition, we study the spectra of those Lyα emitters that are not detected in SMUVS in the same field. We find that of the emission line profiles shown 67% have a single line, 3% a blue bump, and 30% a red tail. The difference in profile distribution could be ascribed to the fainter Lyα luminosities of the MUSE sources not detected in SMUVS and an intrinsically different mass distribution. Finally, we search for the presence of galaxy associations using the spectral redshifts. The integral coverage of MUSE reveals that these associations are 20 times more likely than what is derived from all the other existing spectral data in COSMOS, which is biased by target pre-selection.

Tracing the quenching history of cluster galaxies in the EAGLE simulation

ABSTRACT We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) hydrodynamical simulation to trace the quenching history of galaxies in its 10 most massive clusters. We use two criteria to identify moments when galaxies suffer significant changes in their star formation activity: (i) the instantaneous star formation rate (SFR) strongest drop, $\Gamma _{\rm SFR}^{\rm SD}$, and (ii) a ‘quenching’ criterion based on a minimum threshold for the specific SFR of ≲10$^{-11}\,\rm yr^{-1}$. We find that a large fraction of galaxies (${\gtrsim} 60\,{\rm per\,cent}$) suffer their $\Gamma _{\rm SFR}^{\rm SD}$ outside the cluster’s R200. This ‘pre-processed’ population is dominated by galaxies that are either low mass and centrals or inhabit low-mass hosts (1010.5 ≲ Mhost ≲ 1011.0 M⊙). The host mass distribution is bimodal, and galaxies that suffered their $\Gamma _{\rm SFR}^{\rm SD}$ in massive hosts ($10^{13.5} \lesssim M_{\rm host} \lesssim 10^{14.0}\, \mathrm{M}_{\odot }$) are mainly processed within the clusters. Pre-processing mainly limits the total stellar mass with which galaxies arrive in the clusters. Regarding quenching, galaxies preferentially reach this state in high-mass haloes ($10^{13.5} \lesssim M_{\rm host} \lesssim 10^{14.5}\, \mathrm{M}_{\odot }$). The small fraction of galaxies that reach the cluster already quenched have also been pre-processed, linking both criteria as different stages in the quenching process of those galaxies. For the z = 0 satellite populations, we find a sharp rise in the fraction of quenched satellites at the time of first infall, highlighting the role played by the dense cluster environment. Interestingly, the fraction of pre-quenched galaxies rise with final cluster mass. This is a direct consequence of the hierarchical cosmological model used in these simulations.

Predicting Lyα escape fractions with a simple observable

Lyman-α (Lyα) is intrinsically the brightest line emitted from active galaxies. While it originates from many physical processes, for star-forming galaxies the intrinsic Lyα luminosity is a direct tracer of the Lyman-continuum (LyC) radiation produced by the most massive O- and early-type B-stars (M⋆ ≳ 10 M⊙) with lifetimes of a few Myrs. As such, Lyα luminosity should be an excellent instantaneous star formation rate (SFR) indicator. However, its resonant nature and susceptibility to dust as a rest-frame UV photon makes Lyα very hard to interpret due to the uncertain Lyα escape fraction, fesc, Lyα. Here we explore results from the CAlibrating LYMan-α with Hα (CALYMHA) survey at z = 2.2, follow-up of Lyα emitters (LAEs) at z = 2.2 − 2.6 and a z ∼ 0−0.3 compilation of LAEs to directly measure fesc, Lyα with Hα. We derive a simple empirical relation that robustly retrieves fesc, Lyα as a function of Lyα rest-frame EW (EW0): fesc,Lyα = 0.0048 EW0[Å] ± 0.05 and we show that it constrains a well-defined anti-correlation between ionisation efficiency (ξion) and dust extinction in LAEs. Observed Lyα luminosities and EW0 are easy measurable quantities at high redshift, thus making our relation a practical tool to estimate intrinsic Lyα and LyC luminosities under well controlled and simple assumptions. Our results allow observed Lyα luminosities to be used to compute SFRs for LAEs at z ∼ 0−2.6 within ±0.2 dex of the Hα dust corrected SFRs. We apply our empirical SFR(Lyα,EW0) calibration to several sources at z ≥ 2.6 to find that star-forming LAEs have SFRs typically ranging from 0.1 to 20 M⊙ yr−1 and that our calibration might be even applicable for the most luminous LAEs within the epoch of re-ionisation. Our results imply high ionisation efficiencies (log10[ξion/Hz erg−1] = 25.4−25.6) and low dust content in LAEs across cosmic time, and will be easily tested with future observations with JWST which can obtain Hα and Hβ measurements for high-redshift LAEs.

Suppressed CO emission and high G/D ratios in z = 2 galaxies with sub-solar gas-phase metallicity

ABSTRACT We study a population of significantly sub-solar enrichment galaxies at z = 1.99, to investigate how molecular gas, dust, and star formation relate in low-metallicity galaxies at the peak epoch of star formation. We target our sample with several deep Atacama Large Millimeter/submillimeter Array and Very Large Array datasets, and find no individual detections of CO[4–3], CO[1–0], or dust, in stark contrast to the >60 per cent detection rate expected for solar-enrichment galaxies with these MS H α star formation rates (SFRs). We find that both low- and high-density molecular gas (traced by CO[1–0] and CO[4–3], respectively) are affected by the low enrichment, showing sample average (stacked) luminosity deficits >0.5–0.7 dex below expectations. This is particularly pertinent for the use of high-J CO emission as a proxy of instantaneous SFR. Our individual galaxy data and stacked constraints point to a strong inverse dependence ∝ Zγ of gas-to-dust ratios (G/D) and CO-to-H2 conversion factors (αCO) on metallicity at z ∼ 2, with γG/D <−2.2 and $\gamma _{\alpha _{\rm CO}}\lt $−0.8, respectively. We quantify the importance of comparing G/D and αCO versus metallicity trends from the literature on a common, suitably normalized metallicity scale. When accounting for systematic offsets between different metallicity scales, our z ∼ 2 constraints on these scaling relations are consistent with the corresponding relations for local galaxies. However, among those local relations, we favour those with a steep/double power-law dependence of G/D on metallicity. Finally, we discuss the implications of these findings for (a) gas mass measurements for sub-M* galaxies, and (b) efforts to identify the characteristic galaxy mass scale contributing most to the comoving molecular gas density at z = 2.