Rm SFR Research Articles

Overcoming confusion noise with hyperspectral imaging from PRIMAger

ABSTRACT The PRobe far-Infrared Mission for Astrophysics (PRIMA) concept aims to perform mapping with spectral coverage and sensitivities inaccessible to previous FIR space telescopes. PRIMA’s imaging instrument, PRIMAger, provides unique hyperspectral imaging simultaneously covering 25–235 µm. We synthesize images representing a deep, 1500 h deg−2 PRIMAger survey, with realistic instrumental and confusion noise. We demonstrate that we can construct catalogues of galaxies with a high purity (>95 per cent) at a source density of 42 k deg−2 using PRIMAger data alone. Using the XID+ deblending tool, we show that we measure fluxes with an accuracy better than 20 per cent to flux levels of 0.16, 0.80, 9.7, and 15 mJy at 47.4, 79.7, 172, and 235 µm, respectively. These are a factor of ∼2 and ∼3 fainter than the classical confusion limits for 72–96 and 126–235 µm, respectively. At $1.5 \le z \le 2$, we detect and accurately measure fluxes in 8–10 of the 10 channels covering 47–235 µm for sources with $2 \lesssim \log ({\rm SFR}) \lesssim 2.5$, a 0.5 dex improvement on what might be expected from the classical confusion limit. Recognizing that PRIMager will operate in a context where high-quality data will be available at other wavelengths, we investigate the benefits of introducing additional prior information. We show that by introducing even weak prior flux information when employing a higher source density catalogue (more than one source per beam), we can obtain accurate fluxes an order of magnitude below the classical confusion limit for 96–235 µm.

Dense stellar clump formation driven by strong quasar winds in the FIRE cosmological hydrodynamic simulations

ABSTRACT We investigate the formation of dense stellar clumps in a suite of high-resolution cosmological zoom-in simulations of a massive, star-forming galaxy at z ∼ 2 under the presence of strong quasar winds. Our simulations include multiphase ISM physics from the Feedback In Realistic Environments (FIRE) project and a novel implementation of hyper-refined accretion disc winds. We show that powerful quasar winds can have a global negative impact on galaxy growth while in the strongest cases triggering the formation of an off-centre clump with stellar mass ${\rm M}_{\star }\sim 10^{7}\, {\rm M}_{\odot }$, effective radius ${\rm R}_{\rm 1/2\, \rm Clump}\sim 20\, {\rm pc}$, and surface density $\Sigma _{\star } \sim 10^{4}\, {\rm M}_{\odot }\, {\rm pc}^{-2}$. The clump progenitor gas cloud is originally not star-forming, but strong ram pressure gradients driven by the quasar winds (orders of magnitude stronger than experienced in the absence of winds) lead to rapid compression and subsequent conversion of gas into stars at densities much higher than the average density of star-forming gas. The AGN-triggered star-forming clump reaches ${\rm SFR} \sim 50\, {\rm M}_{\odot }\, {\rm yr}^{-1}$ and $\Sigma _{\rm SFR} \sim 10^{4}\, {\rm M}_{\odot }\, {\rm yr}^{-1}\, {\rm kpc}^{-2}$, converting most of the progenitor gas cloud into stars in ∼2 Myr, significantly faster than its initial free-fall time and with stellar feedback unable to stop star formation. In contrast, the same gas cloud in the absence of quasar winds forms stars over a much longer period of time (∼35 Myr), at lower densities, and losing spatial coherency. The presence of young, ultra-dense, gravitationally bound stellar clumps in recently quenched galaxies could thus indicate local positive feedback acting alongside the strong negative impact of powerful quasar winds, providing a plausible formation scenario for globular clusters.

DUVET: Resolved direct metallicity measurements in the outflow of starburst galaxy NGC 1569

Abstract We present the results of direct-method metallicity measurements in the disk and outflow of the low-metallicity starburst galaxy NGC 1569. We use Keck Cosmic Web Imager observations to map the galaxy across 54″ (800 pc) along the major axis and 48″ (700 pc) along the minor axis with a spatial resolution of 1″ (∼15 pc). We detect common strong emission lines ([O iii] λ5007, Hβ, [O ii] λ3727) and the fainter [O iii] λ4363 auroral line, which allows us to measure electron temperature (Te) and metallicity. Theory suggests that outflows drive metals out of the disk driving observed trends between stellar mass and gas-phase metallicity. Our main result is that the metallicity in the outflow is similar to that of the disk, Zout/ZISM ≈ 1. This is consistent with previous absorption line studies in higher mass galaxies. Assumption of a mass-loading factor of $\dot{M}_{\rm out}/{\rm SFR}\sim 3$ makes the metal-loading of NGC 1569 consistent with expectations derived from the mass-metallicity relationship. Our high spatial resolution metallicity maps reveal a region around a supermassive star cluster (SSC-B) with distinctly higher metallicity and higher electron density, compared to the disk. Given the known properties of SSC-B the higher metallicity and density of this region are likely the result of star formation-driven feedback acting on the local scale. Overall, our results are consistent with the picture in which metal-enriched winds pollute the circumgalactic medium surrounding galaxies, and thus connect the small-scale feedback processes to large-scale properties of galaxy halos.

Properties of the brightest young stellar clumps in extremely lensed galaxies at redshifts 4 to 5

ABSTRACT We study the populations of stellar clumps in three high-redshift galaxies, at z = 4.92, 4.88, and 4.03, gravitationally lensed by the foreground galaxy clusters MS1358, RCS0224, and MACS0940, respectively. The lensed galaxies consist of multiple counter-images with large magnifications, mostly above $\mu > 5$ and in some cases reaching $\mu > 20$. We use rest-frame UV observations from the HST to extract and analyse their clump populations, counting 10, 3, and 11 unique sources, respectively. Most of the clumps have derived effective radii in the range $R_{\rm eff}=10\!-\!100$ pc, with the smallest one down to 6 pc, i.e. consistent with the sizes of individual stellar clusters. Their UV magnitudes correspond to $\rm SFR_{UV}$ mostly in the range $0.1\!-\!1\ {\rm M_\odot \, yr}^{-1}$; the most extreme ones, reaching ${\rm SFR_{UV}}=5\ {\rm M_\odot \, yr}^{-1}$ are among the UV-brightest compact ($R_{\rm eff} < 100$ pc) star-forming regions observed at any redshift. Clump masses span a broad range from 106 to $10^9\,{\rm M}_\odot$; stellar mass surface densities are comparable and in many cases larger than the ones of local stellar clusters, while being typically 10 times larger in size. By compiling published properties of clump populations at similar spatial resolution between redshifts 0 and 5, we find a tentative evolution of $\Sigma_{\rm SFR}$ and $\Sigma _{M_\star }$ with redshift, especially when very compact clumps ($R_{\rm eff}\leqslant 20$ pc) are considered. We suggest that these trends with redshift reflect the changes in the host galaxy environments where clumps form. Comparisons with the local universe clumps/star clusters shows that, although rare, conditions for elevated clump $\Sigma_{\rm SFR}$ and $\Sigma _{M_\star }$ can be found.

Obscuration beyond the nucleus: infrared quasars can be buried in extreme compact starbursts

ABSTRACT In the standard quasar model, the accretion disc obscuration is due to the canonical dusty torus. Here, we argue that a substantial part of the quasar obscuration can come from the interstellar medium (ISM) when the quasars are embedded in compact starbursts. We use an obscuration-unbiased sample of 578 infrared (IR) quasars at z ≈ 1–3 and archival Atacama Large Millimetre/submillimetre Array submillimetre host galaxy sizes to investigate the ISM contribution to the quasar obscuration. We calculate star formation rates (SFR) and ISM column densities for the IR quasars and a control sample of submillimetre galaxies (SMGs) not hosting quasar activity and show that: (1) the quasar obscured fraction is constant up to $\rm SFR\approx 300 \: {\rm M}_{\odot } \: yr^{-1}$, and then increases towards higher SFR, suggesting that the ISM obscuration plays a significant role in starburst host galaxies, and (2) at $\rm SFR\gtrsim 300 \: {\rm M}_{\odot } \: yr^{-1}$, the SMGs and IR quasars have similarly compact submillimetre sizes ($R_{\rm e}\approx 0.5{\!-\!}3\,\mathrm{ kpc}$) and consequently, the ISM can heavily obscure the quasar, even reaching Compton-thick ($N_{\rm H}\gt 10^{24} \rm \: cm^{-2}$) levels in extreme cases. Based on our results, we infer that ${\approx} 10{\!-\!}30~{{ \rm per\ cent}}$ of the IR quasars with $\rm SFR\gtrsim 300 \: {\rm M}_{\odot } \: yr^{-1}$ are obscured solely by the ISM.

Fuelling the nuclear ring of NGC 1097

ABSTRACT Galactic bars can drive cold gas inflows towards the centres of galaxies. The gas transport happens primarily through the so-called bar dust lanes, which connect the galactic disc at kpc scales to the nuclear rings at hundreds of pc scales much like two gigantic galactic rivers. Once in the ring, the gas can fuel star formation activity, galactic outflows, and central supermassive black holes. Measuring the mass inflow rates is therefore important to understanding the mass/energy budget and evolution of galactic nuclei. In this work, we use CO datacubes from the PHANGS-ALMA survey and a simple geometrical method to measure the bar-driven mass inflow rate on to the nuclear ring of the barred galaxy NGC 1097. The method assumes that the gas velocity in the bar lanes is parallel to the lanes in the frame co-rotating with the bar, and allows one to derive the inflow rates from sufficiently sensitive and resolved position–position–velocity diagrams if the bar pattern speed and galaxy orientations are known. We find an inflow rate of $\dot{M}=(3.0 \pm 2.1)\, \rm M_\odot \, yr^{-1}$ averaged over a time span of 40 Myr, which varies by a factor of a few over time-scales of ∼10 Myr. Most of the inflow appears to be consumed by star formation in the ring, which is currently occurring at a star formation rate (SFR) of $\simeq\!1.8\!-\!2 \, \rm M_\odot \, yr^{-1}$, suggesting that the inflow is causally controlling the SFR in the ring as a function of time.

The JCMT nearby galaxies legacy survey: SCUBA-2 observations of nearby galaxies

ABSTRACT We present 850 $\mu$m observations of a sample of 8 nearby spiral galaxies, made using the SCUBA-2 camera on the James Clerk Maxwell Telescope (JCMT) as part of the JCMT Nearby Galaxies Legacy Survey (NGLS). We corrected our data for the presence of the 12CO J = 3 → 2 line in the SCUBA-2 850 $\mu$m bandwidth using NGLS HARP data, finding a typical 12CO contribution of ∼20 per cent. We measured dust column densities, temperatures, and opacity indices by fitting spectral energy distributions constructed from SCUBA-2 and archival Herschel observations, and used archival GALEX and Spitzer data to make maps of surface density of star formation ($\Sigma _{\small {\rm SFR}}$). Typically, comparing SCUBA-2-derived H2 surface densities ($\Sigma _{\rm H_2}$) to $\Sigma _{\small {\rm SFR}}$ gives shallow star formation law indices within galaxies, with SCUBA-2-derived values typically being sublinear and Herschel-derived values typically being broadly linear. This difference is likely due to the effects of atmospheric filtering on the SCUBA-2 data. Comparing the mean values of $\Sigma _{\rm H_2}$ and $\Sigma _{\small {\rm SFR}}$ of the galaxies in our sample returns a steeper star formation law index, broadly consistent with both the Kennicutt–Schmidt value of 1.4 and linearity. Our results show that a SCUBA-2 detection is a good predictor of star formation. We suggest that Herschel emission traces gas in regions which will form stars on time-scales ∼5 − 100 Myr, comparable to the star formation time-scale traced by GALEX and Spitzer data, while SCUBA-2 preferentially traces the densest gas within these regions, which likely forms stars on shorter time-scales.

MASCOT: molecular gas depletion times and metallicity gradients – evidence for feedback in quenching active galaxies

ABSTRACT We present results from the first public data release of the MaNGA-ARO Survey of CO Targets (MASCOT), focusing our study on galaxies whose star formation rates and stellar masses place them below the ridge of the star-forming main sequence. In optically selected type 2 AGN/low-ionization nuclear emission regions (LINERs)/Composites, we find an empirical relation between gas-phase metallicity gradients ∇Z and global molecular gas depletion times $t_{\rm dep} = M_{\rm H_2} /{\rm SFR}$ with ‘more quenched’ systems showing flatter/positive gradients. Our results are based on the O3N2 metallicity diagnostic (applied to star-forming regions within a given galaxy), which was recently suggested to also be robust against emission by diffuse ionized gas (DIG) and LINERs. We conduct a systematic investigation into possible drivers of the observed ∇Z − tdep relation (ouflows, gas accretion, in situ star formation, mergers, and morphology). We find a strong relation between ∇Z or tdep and centralized outflow strength traced by the [O iii] velocity broadening. We also find signatures of suppressed star formation in the outskirts in AGN-like galaxies with long depletion times and an enhancement of metals in the outer regions. We find no evidence of inflows impacting the metallicity gradients, and none of our results are found to be significantly affected by merger activity or morphology. We thus conclude that the observed ∇Z–tdep relation may stem from a combination of metal redistribution via weak feedback, and a connection to in situ star formation via a resolved mass-metallicity–SFR relation.

Decoding NGC 628 with radiative transfer methods

ABSTRACT We present an axi-symmetric model for the ultraviolet (UV)-to-submillimetre (submm) images of the nearly face-on spiral galaxy NGC 628. It was calculated using a radiative transfer (RT) code, accounting for the absorption and re-emission of starlight by dust in the interstellar medium of this galaxy. The code incorporates emission from Polycyclic Aromatic Hydrocarbons, anisotropic scattering, and stochastic heating of the grains. This is the second successful modelling of a face-on spiral galaxy with RT methods, whereby the large-scale geometry of stars and dust is self-consistently determined. The solution was obtained by fitting azimuthally averaged profiles in the UV, optical, and submm. The model predicts remarkably well all characteristics of the profiles, including the increase by a factor of 1.8 of the scale length of the infrared emissivity between 70 and 500 $\mu$m. We find that NGC 628 did not undergo an efficient inside-out disc growth, as predicted by semi-analytical hierarchical models for galaxy formation. We also find large amounts of dust grains at large radii, which could involve efficient transport mechanisms from the inner disc. Our results show that $71{{\ \rm per\ cent}}$ of the dust emission in NGC 628 is powered by the young stellar populations, with the old stellar populations from the bulge contributing $65{{\ \rm per\ cent}}$ to the heating of the dust in the central region (R < 0.5 kpc). The derived star formation rate is $\rm SFR=2.00\pm 0.15\, {\rm M}_{\odot }{\rm yr}^{-1}$.

The ALMA REBELS Survey. Epoch of Reionization giants: Properties of dusty galaxies at z ≈ 7

ABSTRACT We analyse FIR dust continuum measurements for 14 galaxies (redshift z ≈ 7) in the ALMA Reionization Era Bright Emission Line Survey (REBELS) Large Program to derive their physical properties. Our model uses three input data, i.e. (a) the UV spectral slope, β, (b) the observed UV continuum flux at 1500 Å, F1500, (c) the observed continuum flux at $\approx 158\, \mu$m, F158, and considers Milky Way (MW) and SMC extinction curves, along with different dust geometries. We find that REBELS galaxies have 28−90.5 per cent of their star formation obscured; the total (UV+IR) star formation rates are in the range $31.5 \lt {\rm SFR}/({\rm M}_\odot \, {\rm yr}^{-1}) \lt 129.5$. The sample-averaged dust mass and temperature are $(1.3\pm 1.1)\times 10^7 \, \mathrm{M}_\odot$ and 52 ± 11 K, respectively. However, in some galaxies dust is particularly abundant (REBELS-14, $M^{\prime }_{\rm d} \approx 3.4 \times 10^7 \, \mathrm{M}_\odot$), or hot (REBELS-18, $T^{\prime }_{\rm d} \approx 67$ K). The dust distribution is compact (<0.3 kpc for 70 per cent of the galaxies). The inferred dust yield per supernova is $0.1 \le y_{\rm d}/\, \mathrm{M}_\odot \le 3.3$, with 70 per cent of the galaxies requiring $y_{\rm d} \lt 0.25 \, \mathrm{M}_\odot$. Three galaxies (REBELS-12, 14, 39) require $y_{\rm d} \gt 1 \, \mathrm{M}_\odot$, which is likely inconsistent with pure SN production, and might require dust growth via accretion of heavy elements from the interstellar medium. With the SFR predicted by the model and a MW extinction curve, REBELS galaxies detected in [C ii] nicely follow the local LCII−SFR relation, and are approximately located on the Kennicutt–Schmidt relation. The sample-averaged gas depletion time is $0.11\, y_{\rm P}^{-2}$ Gyr, where yP is the ratio of the gas-to-stellar distribution radius. For some systems, a solution simultaneously matching the observed (β, F1500, F158) values cannot be found. This occurs when the index Im = (F158/F1500)/(β − βint), where βint is the intrinsic UV slope, exceeds $I_m^{*}\approx 1120$ for an MW curve. For these objects, we argue that the FIR and UV emitting regions are not co-spatial, questioning the use of the IRX–β relation.

C ii] Haloes in ALPINE galaxies: smoking-gun of galactic outflows?

ABSTRACT ALMA observations have revealed that many high-redshift galaxies are surrounded by extended (10–15 kpc) [C ii]-emitting haloes that are not predicted by even the most advanced zoom-in simulations. Using a semi-analytical model, in a previous work we suggested that such haloes are produced by starburst-driven, catastrophically cooling outflows. Here, we further improve the model and compare its predictions with data from seven star-forming ($10\lesssim \rm SFR/{\rm M}_{\odot }\, yr^{-1}\lesssim 100$) galaxies at z = 4–6, observed in the ALPINE survey. We find that (a) detected [C ii] haloes are a natural by-product of starburst-driven outflows; (b) the outflow mass loading factors are in the range 4 ≲ η ≲ 7, with higher η values for lower mass, lower star formation rate systems, and scale with stellar mass as $\eta \propto M_*^{-0.43}$, consistently with the momentum-driven hypothesis. Our model suggests that outflows are widespread phenomena in high-z galaxies. However, in low-mass systems the halo extended [C ii] emission is likely too faint to be detected with the current levels of sensitivity.

FOREVER22: galaxy formation in protocluster regions

ABSTRACT We present results from a new cosmological hydrodynamics simulation campaign of protocluster (PC) regions, FOREVER22: FORmation and EVolution of galaxies in Extremely overdense Regions motivated by SSA22. The simulations cover a wide range of cosmological scales using three different zoom set-ups in a parent volume of $(714.2~\rm cMpc)^{3}$: PCR (Proto-Cluster Region; V = (28.6 cMpc)3, SPH particle mass, mSPH = 4.1 × 106 M⊙, and final redshift, zend = 2.0), BCG (Brightest proto-Cluster Galaxy; V ∼ (10 cMpc)3, mSPH = 5.0 × 105 M⊙ and zend = 4.0), and First (V ∼ (3 cMpc)3, mSPH = 7.9 × 103 M⊙ and zend = 9.5) runs, that allow us to focus on different aspects of galaxy formation. In the PCR runs, we follow 10 PCs, each harbouring 1–4 SMBHs with ${\rm M_{\rm BH}}\ge 10^{9}~{\rm M_{\odot }}$. One of the PC cores shows a spatially close arrangement of seven starburst galaxies with ${\rm SFR} \gtrsim 100~{\rm {\rm M_{\odot }}~{\rm yr^{-1}}}$ each, that are dust-obscured and would appear as submillimetre galaxies with flux ≳1 mJy at $1.1~ \rm mm$ in observations. The BCG runs show that the total SFRs of haloes hosting BCGs are affected by AGN feedback, but exceed $1000~{\rm {\rm M_{\odot }}~{\rm yr^{-1}}}$ at z ≲ 6. The First runs resolve mini-haloes hosting population (Pop) III stars and we show that, in PC regions, the dominant stellar population changes from Pop III to Pop II at z ≳ 20, and the first galaxies with ${\rm SFR} \gtrsim 18~{\rm {\rm M_{\odot }}~{\rm yr^{-1}}}$ form at z ∼ 10. These can be prime targets for future observations with the James Webb Space Telescope. Our simulations successfully reproduce the global star formation activities in observed PCs and suggest that PCs can kickstart cosmic reionization.

The UV-brightest Lyman continuum emitting star-forming galaxy

ABSTRACT We report the discovery of J0121+0025, an extremely luminous and young star-forming galaxy (MUV = −24.11, log[$L_{\rm Ly \alpha } / \rm erg~s^{-1}] = 43.8$) at z = 3.244 showing copious Lyman continuum (LyC) leakage ($f_{\rm esc, abs} \approx 40{{\ \rm per\ cent}}$). High signal-to-noise ratio rest-frame UV spectroscopy with the Gran Telescopio Canarias reveals a high significance (7.9σ) emission below the Lyman limit (<912 Å), with a flux density level f900 = 0.78 ± 0.10μJy, and strong P-Cygni in wind lines of O vi 1033 Å, N v 1240 Å, and C iv 1550 Å that are indicative of a young age of the starburst (<10 Myr). The spectrum is rich in stellar photospheric features, for which a significant contribution of an AGN at these wavelengths is ruled out. Low-ionization interstellar medium (ISM) absorption lines are also detected, but are weak ($EW_{0} \rm \simeq 1$ Å) and show large residual intensities, suggesting a clumpy geometry of the gas with a non-unity covering fraction or a highly ionized ISM. The contribution of a foreground and AGN contamination to the LyC signal is unlikely. Deep optical to Spitzer/IRAC 4.5 μm imaging show that the spectral energy distribution of J0121+0025 is dominated by the emission of the young starburst, with log($M_{\star }^{\rm burst}/M_{\odot }) = 9.9\pm 0.1$ and $\rm SFR = 981\pm 232$ M⊙ yr−1. J0121+0025 is the most powerful LyC emitter known among the star-forming galaxy population. The discovery of such luminous and young starburst leaking LyC radiation suggests that a significant fraction of LyC photons can escape in sources with a wide range of UV luminosities and are not restricted to the faintest ones as previously thought. These findings might shed further light on the role of luminous starbursts to the cosmic reionization.

Infrared emission of z ∼ 6 galaxies: AGN imprints

ABSTRACT We investigate the infrared (IR) emission of high-redshift (z ∼ 6), highly star-forming (${{\rm SFR}\gt 100\,{\rm M}_{\odot }\, {\rm yr}^{-1}}$) galaxies, with/without active galactic nuclei (AGN), using a suite of cosmological simulations featuring dust radiative transfer. Synthetic spectral energy distributions (SEDs) are used to quantify the relative contribution of stars/AGN to dust heating. In dusty (Md ≳ 3 × 107 M⊙) galaxies, ≳50–90 per cent of the ultraviolet (UV) radiation is obscured by dust inhomogeneities on scales ≳100 pc. In runs with AGN, a clumpy, warm (≈250 K) dust component coexists with a colder (≈60 K) and more diffuse one, heated by stars. Warm dust provides up to ${50 {{\ \rm per\ cent}}}$ of the total infrared (IR) luminosity, but only ${\lesssim}0.1 {{\ \rm per\ cent}}$ of the total mass content. The AGN boosts the MIR flux by 10–100 times with respect to star-forming galaxies, without significantly affecting the far-IR. Our simulations successfully reproduce the observed SED of bright (MUV ∼ −26) z ∼ 6 quasars, and show that these objects are part of complex, dust-rich merging systems, containing multiple sources (accreting black holes and/or star-forming galaxies) in agreement with recent HST and ALMA observations. Our results show that the proposed ORIGINS missions will be able to investigate the mid-IR (MIR) properties of dusty star-forming galaxies and to obtain good-quality spectra of bright quasars at z ∼ 6. Finally, the MIR-to-FIR flux ratio of faint (MUV ∼ −24) AGN is >10 times higher than for normal star-forming galaxies. This implies that combined JWST/ORIGINS/ALMA observations will be crucial to identify faint and/or dust-obscured AGN in the distant Universe.

Constraints on the [C ii] luminosity of a proto-globular cluster at z ∼ 6 obtained with ALMA

ABSTRACT We report on ALMA observations of D1, a system at z ∼ 6.15 with stellar mass $M_{*} \sim 10^7 \, \mathrm{M}_{\odot }$ containing globular cluster (GC) precursors, strongly magnified by the galaxy cluster MACS J0416.1-2403. Since the discovery of GC progenitors at high redshift, ours is the first attempt to probe directly the physical properties of their neutral gas through infrared observations. A careful analysis of our data set, performed with a suitable procedure designed to identify faint narrow lines and which can test various possible values for the unknown linewidth value, allowed us to identify a 4σ tentative detection of [C ii] emission with intrinsic luminosity $L_{\rm [C\, \rm {\small II}]}=(2.9 \pm 1.4)~10^6 \, {\it L}_{\odot }$, one of the lowest values ever detected at high redshift. This study offers a first insight on previously uncharted regions of the $L_{\rm [C\, \rm {\small II}]}{-}{\rm SFR}$ relation. Despite large uncertainties affecting our measure of the star formation rate, if taken at face value our estimate lies more than ∼1 dex below the values observed in local and high redshift systems. Our weak detection indicates a deficiency of [C ii] emission, possibly ascribed to various explanations, such as a low-density gas and/or a strong radiation field caused by intense stellar feedback, and a low metal content. From the non-detection in the continuum, we derive constraints on the dust mass, with 3σ upper limit values as low as ∼ a few 104 M⊙, consistent with the values measured in local metal-poor galaxies.

Starbursting [O iii] emitters and quiescent [C ii] emitters in the reionization era

ABSTRACT Recent observations have successfully detected [O iii] $88.3\, {\rm \mu m}$ and [C ii] $157.6\, {\rm \mu m}$ lines from galaxies in the early Universe with the Atacama Large Millimeter Array. Combining cosmological hydrodynamic simulations and radiative transfer calculations, we present relations between the metal line emission and galaxy evolution at z = 6–15. We find that galaxies during their starburst phases have high [O iii] luminosity of ${\sim}10^{42}~\rm erg~s^{-1}$. Once supernova feedback quenches star formation, [O iii] luminosities rapidly decrease and continue to be zero for ${\sim}100\, {\rm Myr}$. The slope of the relation between $\log {(\rm SFR/\rm M_{\odot }~ yr^{-1})}$ and $\log {(L_{\rm [O\, \small {III}]}/\mathrm{L}_{\odot })}$ at z = 6–9 is 1.03, and 1.43 for $\log {(L_{\rm [C\, \small {II}]}/\mathrm{L}_{\odot })}$. As gas metallicity increases from sub-solar to solar metallicity by metal enrichment from star formation and feedback, the line luminosity ratio $L_{\rm [O\, \small {III}]} / L_{\rm [C\, \small {II}]}$ decreases from ∼10 to ∼1 because the O/C abundance ratio decreases due to carbon-rich winds from AGB stars and the mass ratio of H ii to H i regions decreases due to rapid recombination. Therefore, we suggest that the combination of [O iii] and [C ii] lines is a good probe to investigate the relative distribution of ionized and neutral gas in high-z galaxies. In addition, we show that deep [C ii] observations with a sensitivity of ∼10−2 mJy arcsec−2 can probe the extended neutral gas discs of high-z galaxies.

Velocity dispersion in the interstellar medium of early galaxies

ABSTRACT We study the structure of spatially resolved, line-of-sight velocity dispersion for galaxies in the Epoch of Reionization (EoR) traced by [C $\scriptstyle \rm II$] $158\, \mu \rm {m}$ line emission. Our laboratory is a simulated prototypical Lyman-break galaxy, ‘Freesia, part of the serra suite’. The analysis encompasses the redshift range 6 < z < 8, when Freesia is in a very active assembling phase. We build velocity dispersion maps for three dynamically distinct evolutionary stages (Spiral Disc at z = 7.4, Merger at z = 8.0, and Disturbed Disc at z = 6.5) using [C $\scriptstyle \rm II$] hyperspectral data cubes. We find that, at a high spatial resolution of 0.005 arcsec (≃30 pc), the luminosity-weighted average velocity dispersion is $\sigma _{\rm {CII}}\simeq 23{\text {--}}38\, {\rm km\, s^{-1}}$ with the highest value belonging to the highly structured Disturbed Disc stage. Low-resolution observations tend to overestimate σC ii values due to beam smearing effects that depend on the specific galaxy structure. For an angular resolution of 0.02 arcsec (0.1 arcsec), the average velocity dispersion is $16{\!-\!}34{{\ \rm per\ cent}}$ ($52{\!-\!}115{{\ \rm per\ cent}}$) larger than the actual one. The [C $\scriptstyle \rm II$] emitting gas in Freesia has a Toomre parameter $\mathcal {Q}\simeq 0.2$ and rotational-to-dispersion ratio of vc/σ ≃ 7 similar to that observed in z = 2−3 galaxies. The primary energy source for the velocity dispersion is due to gravitational processes, such as merging/accretion events; energy input from stellar feedback is generally sub-dominant ($\lt 10{{\ \rm per\ cent}}$). Finally, we find that the resolved σC ii−ΣSFR relation is relatively flat for $0.02\lt {\Sigma }_{\rm SFR}/{\rm M}_{\odot }\rm {yr}^{-1} {\rm kpc}^{-2} \lt 30$, with the majority of data lying on the derived analytical relation $\sigma \propto \Sigma _{\rm SFR}^{5/7}$. At high SFR, the increased contribution from stellar feedback steepens the relation, and σC ii rises slightly.

A census of ultraluminous X-ray sources in the local Universe

ABSTRACTUsing the Chandra Source Catalog 2.0 and a newly compiled catalogue of galaxies in the local Universe, we deliver a census of ultraluminous X-ray source (ULX) populations in nearby galaxies. We find 629 ULX candidates in 309 galaxies with distance smaller than 40 Mpc. The foreground/background contamination is $\sim \! 20{{\ \rm per\ cent}}$. The ULX populations in bona fide star-forming galaxies scale on average with star formation rate and stellar mass (M⋆) such that the number of ULXs per galaxy is $0.45^{+0.06}_{-0.09}\times \frac{\rm SFR}{\rm M_\odot \, yr^{-1}}{+}3.3^{+3.8}_{-3.2}\times \frac{M_\star }{\rm M_\odot }$. The scaling depends strongly on the morphological type. This analysis shows that early spiral galaxies contain an additional population of ULXs that scales with M⋆. We also confirm the strong anticorrelation of the ULX rate with the host galaxy’s metallicity. In the case of early-type galaxies, we find that there is a non-linear dependence of the number of ULXs with M⋆, which is interpreted as the result of star formation history differences. Taking into account age and metallicity effects, we find that the predictions from X-ray binary population synthesis models are consistent with the observed ULX rates in early-type galaxies, as well as spiral/irregular galaxies.

A radiative transfer model for the spiral galaxy M33★

ABSTRACT We present the first radiative transfer (RT) model of a non-edge-on disc galaxy in which the large-scale geometry of stars and dust is self-consistently derived through the fitting of multiwavelength imaging observations from the ultraviolet to the submm. To this end, we used the axisymmetric RT model of Popescu et al. and a new methodology for deriving geometrical parameters, and applied this to decode the spectral energy distribution (SED) of M33. We successfully account for both the spatial and spectral energy distribution, with residuals typically within $7{{\ \rm per\ cent}}$ in the profiles of surface brightness and within $8{{\ \rm per\ cent}}$ in the spatially integrated SED. We predict well the energy balance between absorption and re-emission by dust, with no need to invoke modified grain properties, and we find no submm emission that is in excess of our model predictions. We calculate that $80\pm 8{{\ \rm per\ cent}}$ of the dust heating is powered by the young stellar populations. We identify several morphological components in M33, a nuclear, an inner, a main and an outer disc, showing a monotonic trend in decreasing star formation surface density (ΣSFR) from the nuclear to the outer disc. In relation to surface density of stellar mass, the ΣSFR of these components defines a steeper relation than the ‘main sequence’ of star-forming galaxies, which we call a ‘structurally resolved main sequence’. Either environmental or stellar feedback mechanisms could explain the slope of the newly defined sequence. We find the star formation rate to be ${\rm SFR}=0.28^{+0.02}_{-0.01}{\rm M}_{\odot }{\rm yr}^{-1}$.

An ALMA survey of the SCUBA-2 cosmology legacy survey UKIDSS/UDS field: Dust attenuation in high-redshift Lyman-break galaxies

ABSTRACT We analyse 870 $\mu$m Atacama Large Millimetre Array (ALMA) dust continuum detections of 41 canonically selected $z$ ≃ 3 Lyman-break galaxies (LBGs), as well as 209 ALMA-undetected LBGs, in follow-up of SCUBA-2 mapping of the UKIDSS Ultra Deep Survey (UDS) field. We find that our ALMA-bright LBGs lie significantly off the local IRX-beta relation and have relatively bluer rest-frame UV slopes (as parametrized by β), given their high values of the ‘infrared excess’ (IRX ≡ LIR/LUV), relative to the average ‘local’ IRX-β relation. We attribute this finding in part to the young ages of the underlying stellar populations but we find that the main reason behind the unusually blue UV slopes are the relatively shallow slopes of the corresponding dust attenuation curves. We show that, when stellar masses, M*, are being established via SED fitting, it is absolutely crucial to allow the attenuation curves to vary (rather than fixing it on Calzetti-like law), where we find that the inappropriate curves may underestimate the resulting stellar masses by a factor of ≃2–3× on average. In addition, we find these LBGs to have relatively high specific star-formation rates (sSFRs), dominated by the dust component, as quantified via the fraction of obscured star formation $(f_{\rm obs}\equiv {\rm SFR_{\rm IR}/{\rm SFR}_{\rm UV+IR}})$. We conclude that the ALMA-bright LBGs are, by selection, massive galaxies undergoing a burst of a star formation (large sSFRs, driven, for example, by secular or merger processes), with a likely geometrical disconnection of the dust and stars, responsible for producing shallow dust attenuation curves.