Star Formation Rates Of Galaxies Research Articles

Transonic galactic wind model including stellar feedbacks and application to outflows in high/low-z galaxies

Abstract Galactic winds play a crucial role in the ejection of the interstellar medium (ISM) into intergalactic space. This study presents a model that classifies possible transonic solutions of galactic winds in the gravitational potential of the dark matter halo and stellar component under spherically symmetric and steady assumptions. Our model includes injections of mass and energy resulting from supernova feedback along a flow line. The mass flux in galactic winds is a critical factor in determining the acceleration process of the flow and revealing the impact of galactic winds on galaxy evolution. We apply the transonic galactic wind model to the observed outflow velocities of star-forming galaxies to estimate the mass flux. Dividing the mass flux by the star formation rate (SFR) yields the mass loading rate (and mass loading factor), which indicates the entrainment effect of the ISM by the hot gas flow. Our results demonstrate that the mass loading rate is inversely correlated with galaxy mass and SFR. In less massive galaxies (stellar mass ∼107−8 M⊙), the mass loading rate exceeds unity, indicating effective ejection of the ISM into intergalactic space. However, in massive galaxies (stellar mass ∼1010−11 M⊙), the mass loading rate falls below unity, meaning that the mass flux cannot exceed the injected mass by supernovae, thus resulting in ineffective ejection of the ISM.

Arkenstone – I. A novel method for robustly capturing high specific energy outflows in cosmological simulations

ABSTRACT Arkenstone is a new model for multiphase, stellar feedback-driven galactic winds designed for inclusion in coarse resolution cosmological simulations. In this first paper of a series, we describe the features that allow Arkenstone to properly treat high specific energy wind components and demonstrate them using idealized non-cosmological simulations of a galaxy with a realistic circumgalactic medium (CGM), using the arepo code. Hot, fast gas phases with low mass loadings are predicted to dominate the energy content of multiphase outflows. In order to treat the huge dynamic range of spatial scales involved in cosmological galaxy formation at feasible computational expense, cosmological volume simulations typically employ a Lagrangian code or else use adaptive mesh refinement with a quasi-Lagrangian refinement strategy. However, it is difficult to inject a high specific energy wind in a Lagrangian scheme without incurring artificial burstiness. Additionally, the low densities inherent to this type of flow result in poor spatial resolution. Arkenstone addresses these issues with a novel scheme for coupling energy into the transition region between the interstellar medium (ISM) and the CGM, while also providing refinement at the base of the wind. Without our improvements, we show that poor spatial resolution near the sonic point of a hot, fast outflow leads to an underestimation of gas acceleration as the wind propagates. We explore the different mechanisms by which low and high specific energy winds can regulate the star formation rate of galaxies. In future work, we will demonstrate other aspects of the Arkenstone model.

Galaxy Interactions in Filaments and Sheets: Insights from EAGLE Simulations

We study the color and star formation rates of paired galaxies in filaments and sheets using the EAGLE simulations. We find that the major pairs with pair separation <50 kpc are bluer and more star-forming in filamentary environments compared to those hosted in sheet-like environments. This trend reverses beyond a pair separation of ∼50 kpc. The interacting pairs with larger separations (>50 kpc) in filaments are on average redder and low-star-forming compared to those embedded in sheets. The galaxies in filaments and sheets may have different stellar mass and cold gas mass distributions. Using a KS test, we find that for paired galaxies with pair separation <50 kpc, there are no significant differences in these properties in sheets and filaments. The filaments transport gas toward the cluster of galaxies. Some earlier studies find preferential alignment of galaxy pairs with the filament axis. Such alignment of galaxy pairs may lead to different gas accretion efficiency in galaxies residing in filaments and sheets. We propose that the enhancement of star formation rate at smaller pair separation in filaments is caused by the alignment of galaxy pairs. A recent study with SDSS data reports the same findings. The confirmation of these results by the EAGLE simulations suggests that the hydrodynamical simulations are powerful theoretical tools for studying galaxy formation and evolution in the cosmic web.

MULTIWAVELENGTH PROPERTIES OF THE LOW-REDSHIFT ISOLATED GALAXIES WITH ACTIVE NUCLEI MODELLED WITH CIGALE

Using the CIGALE software, we present the preliminary results of a multiwavelength analysis of eighteen low-redshift isolated galaxies with active nuclei (isolated AGNs). This sample was formed by cross-matching the 2MIG isolated AGNs sample with the SDSS DR9 catalog. The host galaxies of this sample have not undergone a merger for at least three billion years, making them a unique laboratory for studying interactions between various astrophysical processes without the complicating factors of merging with other galaxies or the effects of a denser environment. In addition, the study of isolated AGNs can provide valuable information about the evolution and activity of galaxies in the broader context of the distribution of large-scale structures of the Universe. First, we seek to understand how the environment affects the physical processes involved in the accretion of matter onto supermassive black holes in these galaxies. Secondly, to what extent do processes of star formation or degeneration of nuclei activity continue the evolution of these galaxies? Third, how does the localization of isolated AGNs in voids or filaments of a large-scale structure determine the properties of this envi- ronment at the low redshifts? Using observable fluxes from UV to the radio ranges from archival databases of space-born and ground-based observatories (GALEX, SDSS, 2MASS, Spitzer, Hershel, IRAS, WISE, VLA), we estimated the contribution from the emission of an active nucleus to the galaxy’s total emission, the stellar mass, and the star formation rate. The mass of the stellar component falls from 1010 MSun and 1011 MSun. The star formation rate for most galaxies (except UGC 10120) does not exceed 3 MSun per year. The best SED fittings (with χ2 values less than 5) are obtained for the galaxies CGCG248-019 (χ2 = 1.6), CGCG179-005 (χ2 = 1.6), CGCG243-024 (χ2 = 2.6), IC0009 (χ2 = 2.8), MCG+09-25-022 (χ2 = 3.1), UGC10244 (χ2 = 4.1)

ALMA Lensing Cluster Survey: average dust, gas, and star-formation properties of cluster and field galaxies from stacking analysis

ABSTRACT We develop new tools for continuum and spectral stacking of Atacama Large Millimeter/submillimeter Array (ALMA) data, and apply these to the ALMA Lensing Cluster Survey. We derive average dust masses, gas masses, and star-formation rates (SFRs) from the stacked observed 260-GHz continuum of 3402 individually undetected star-forming galaxies, of which 1450 are cluster galaxies and 1952 field galaxies, over three redshift and stellar mass bins (over z = 0–1.6 and log$M_{*} \, [{\rm M}_{\odot }] = 8$–11.7), and derive the average molecular gas content by stacking the emission line spectra in a SFR-selected subsample. The average SFRs and specific SFRs of both cluster and field galaxies are lower than those expected for main-sequence (MS) star-forming galaxies, and only galaxies with stellar mass of log$M_{*} \, [{\rm M}_{\odot }] = 9.35$–10.6 show dust and gas fractions comparable with those in the MS. The ALMA-traced average ‘highly obscured’ SFRs are typically lower than the SFRs observed from optical to near-infrared spectral analysis. Cluster and field galaxies show similar trends in their contents of dust and gas, even when field galaxies were brighter in the stacked maps. From spectral stacking we find a potential CO (J = 4 → 3) line emission (signal-to-noise ratio being ∼4) when stacking cluster and field galaxies with the highest SFRs.

The Mass–Metallicity Relation of Dwarf Galaxies at Cosmic Noon from JWST Observations

We present a study of the mass–metallicity relation (MZR) of 51 dwarf galaxies (M ⋆ ≈ 106.5–109.5 M ⊙) at z = 2–3 from the A2744 and SMACS J0723-3732 galaxy cluster fields. These dwarf galaxies are identified and confirmed by deep JWST/NIRISS imaging and slitless grism spectroscopic observations. By taking advantage of the superior performance of JWST and the gravitational lensing effect, we extend the previous MZR relation at z = 2–3 to a much lower-mass regime down by ≈2.5 orders of magnitude as compared with previous studies. We find that the MZR has a shallower slope at the low-mass end (M ⋆ < 109 M ⊙), with a slope turnover point of ≈109 M ⊙. This implies that the dominating feedback processes in dwarf galaxies may be different from that in massive galaxies. From z = 3, to z = 2, the metallicity of the dwarf galaxies is enhanced by ≈0.09 dex for a given stellar mass, consistent with the mild evolution found in galaxies with higher mass. Furthermore, we confirm the existence of a fundamental metallicity relation (FMR) between the gas-phase metallicity, stellar mass, and star formation rate in dwarf galaxies at z = 2–3. Our derived FMR, which has no significant redshift evolution, can be used as a benchmark to understand the origin of the anticorrelation between the star formation rate and metallicity of dwarf galaxies in the high-z Universe.

Do Minor Interactions Trigger Star Formation in Galaxy Pairs?

We analyze the galaxy pairs in a set of volume limited samples from the Sloan Digital Sky Survey to study the effects of minor interactions on the star formation rate (SFR) and color of galaxies. We carefully design control samples of isolated galaxies by matching the stellar mass and redshift of the minor pairs. The SFR distributions and color distributions in the minor pairs differ from their controls at >99% significance level. We also simultaneously match the control galaxies in stellar mass, redshift and local density to assess the role of the environment. The null hypothesis can be rejected at >99% confidence level even after matching the environment. Our analysis shows a quenching in the minor pairs where the degree of quenching decreases with the increasing pair separation and plateaus beyond 50 kpc. We also prepare a sample of minor pairs with H α line information. We calculate the SFR of these galaxies using the H α line and repeat our analysis. We observe a quenching in the H α sample too. We find that the majority of the minor pairs are quiescent systems that could be quenched due to minor interactions. Combining data from the Galaxy Zoo and Galaxy Zoo 2, we find that only ∼1% galaxies have a dominant bulge, 4%–7% galaxies host a bar and 5%–10% of galaxies show active galactic nucleus (AGN) activity in minor pairs. This indicates that the presence of bulge, bar or AGN activity plays an insignificant role in quenching the galaxies in minor pairs. The more massive companion satisfies the criteria for mass quenching in most of the minor pairs. We propose that the stripping and starvation likely caused the quenching in the less massive companion at a later stage of evolution.

Stochastic star formation in early galaxies: Implications for the James Webb Space Telescope

Contact. The star formation rate (SFR) in high-redshift galaxies is expected due to competing physical processes. This stochastic variability might boost the luminosity of galaxies and might explain the over-abundance seen at z ≳ 10 by the James Webb Space Telescope. Aims. We quantify the amplitude and timescales of this variability and identify the key physical processes. Methods. We selected 245 z = 7.7 galaxies with stellar mass 5 × 106 ≲ M⋆/M⊙ ≲ 5 × 1010 from SERRA, which is a suite of high-resolution radiation-hydrodynamic cosmological simulations. After fitting the average SFR trend, ⟨SFR⟩, we quantified the time-dependent variation, δ(t)≡log[SFR/⟨SFR⟩], for each system and performed a periodogram analysis to search for periodicity modulations. Results. We find that δ(t) is distributed as a zero-mean Gaussian, with standard deviation σδ ≃ 0.24 (corresponding to a UV magnitude s.d. σUV ≃ 0.61) that is independent of M⋆. However, the modulation timescale increases with stellar mass: tδ ∼ (9, 50, 100) Myr for M⋆ ∼ (0.1, 1, 5)×109 M⊙, respectively. These timescales are imprinted on the SFR by different processes: (i) photoevaporation, (ii) supernova explosions, and (iii) cosmological accretion/merging dominating in low-, intermediate-, and high-mass systems, respectively. Conclusions. The predicted SFR variations cannot account for the required z ≳ 10 UV luminosity function boost. Other processes, such as radiation-driven outflows clearing the dust, must then be invoked to explain the enhanced luminosity of super-early systems.

A Value-added COSMOS2020 Catalog of Physical Properties: Constraining Temperature-dependent Initial Mass Function

This work presents and releases a catalog of new photometrically derived physical properties for the ∼105 most well-measured galaxies in the COSMOS field on the sky. Using a recently developed technique, spectral energy distributions are modeled assuming a stellar initial mass function (IMF) that depends on the temperature of gas in star-forming regions. The method is applied to the largest current sample of high-quality panchromatic photometry, the COSMOS2020 catalog, that allows for testing this assumption. It is found that the galaxies exhibit a continuum of IMF and gas temperatures, most of which are bottom-lighter than measured in the Milky Way. As a consequence, the stellar masses and star formation rates of most galaxies here are found to be lower than those measured by traditional techniques in the COSMOS2020 catalog by factors of ∼1.6–3.5 and 2.5–70.0, respectively, with the change being the strongest for the most active galaxies. The resulting physical properties provide new insights into variation of the IMF-derived gas temperature along the star-forming main sequence and at quiescence, produce a sharp and coherent picture of downsizing, as seen from the stellar mass functions, and hint at a possible high-temperature and high-density stage of early galactic evolution.

An H I story of galaxies in Abell 2626 and beyond

Context. To study the effects of environment on galaxies, we use H I observations of galaxies in and around the cluster Abell 2626 (A2626). The cluster can effectively be divided into three different environments: the cluster itself, a group environment in the periphery of the cluster (we call it the Swarm), and substructure in the cluster itself. We use these to study the dependence of the galaxy properties on environment. Aims. We have explored the relation between H I deficiency, H I morphology, and star formation deficiency for the galaxies in and around the A2626 galaxy cluster to investigate the environmental effects on these properties. Methods. To quantify the asymmetries of the outer H I disc of a galaxy, we used 1) three visual classes based on the outermost reliable H I contour (settled, disturbed, and unsettled H I discs), 2) the offset between the H I centre and the optical centre of a galaxy, and 3) the modified asymmetry parameter Amod as defined previously. Results. The H I deficiency of a galaxy is strongly correlated with the projected distance from the centre of A2626. Furthermore, substructure galaxies tend to be more asymmetric than the isolated galaxies in A2626, probably because tidal interactions are more efficient within the substructures than outside the substructures. Moreover, asymmetric, offset, and smaller H I discs are not necessarily the result of the cluster environment because they are also observed in substructures in A2626 and in the Swarm. This signifies that a pre-processing of the H I discs of galaxies in groups or substructures plays an important role, together with the processing in the cluster environment. Finally, the star formation rates for the galaxies in all three environments are slightly lower than the typical star formation rate for normal galaxies, as manifested by their offset from the star formation main sequence. This implies effective gas removal mechanisms in all three environments.

Quantifying the energetics of molecular superbubbles in PHANGS galaxies

Context. Star formation and stellar feedback are interlinked processes that redistribute energy, turbulence, and material throughout galaxies. Because young and massive stars form in spatially clustered environments, they create pockets of expanding gas termed superbubbles, which retain information about the physical processes that drive them. As these processes play a critical role in shaping galaxy discs and regulating the baryon cycle, measuring the properties of superbubbles provides important input for galaxy evolution models. Aims. With the wide coverage and high angular resolution (∼50–150 pc) of the PHANGS–ALMA 12CO (J = 2−1) survey, we can now resolve, identify and characterise a statistically representative number of superbubbles using molecular gas in nearby galaxies. Methods. We identify superbubbles by requiring spatial correspondence between shells in CO with stellar populations identified in PHANGS–HST. Then, by combining the properties of the stellar populations with the CO, we quantify the energetics of the stars and constrain feedback models. We visually find 325 cavities across 18 PHANGS–ALMA galaxies, 88 of which have clear superbubble signatures (unbroken shells, central clusters, kinematic signatures of expansion). We measure their radii and expansion velocities using CO (2–1) to dynamically derive their ages and the mechanical power driving the bubbles, which we use to compute the expected properties of the parent stellar populations driving the bubbles. Results. We find consistency between the predicted and derived stellar ages and masses of the stellar populations if we use a supernova (SN) model that injects energy with a coupling efficiency of ∼10%. Not only does this confirm that molecular gas accurately traces superbubble properties, but it also provides key observational constraints for superbubble models. We also find evidence that the bubbles are sweeping up gas as they expand, and speculate that these sites have the potential to host new generations of stars. Conclusions. This work demonstrates that molecular superbubbles provide novel quantitative constraints on SNe feedback efficiencies and gas clearing times, and represent a promising environment to search for the propagation of star formation, all of which are needed to understand what sets the observed star formation rates in galaxies.

Cosmic-ray driven galactic winds from the warm interstellar medium

ABSTRACT We study the properties of cosmic-ray (CR) driven galactic winds from the warm interstellar medium using idealized spherically symmetric time-dependent simulations. The key ingredients in the model are radiative cooling and CR-streaming-mediated heating of the gas. Cooling and CR heating balance near the base of the wind, but this equilibrium is thermally unstable, leading to a multiphase wind with large fluctuations in density and temperature. In most of our simulations, the heating eventually overwhelms cooling, leading to a rapid increase in temperature and a thermally driven wind; the exception to this is in galaxies with the shallowest potentials, which produce nearly isothermal $T \approx 10^4\,$ K winds driven by CR pressure. Many of the time-averaged wind solutions found here have a remarkable critical point structure, with two critical points. Scaled to real galaxies, we find mass outflow rates $\dot{M}$ somewhat larger than the observed star-formation rate in low-mass galaxies, and an approximately ‘energy-like’ scaling $\dot{M} \propto v_{\rm esc}^{-2}$. The winds accelerate slowly and reach asymptotic wind speeds of only ∼0.4vesc. The total wind power is $\sim 1~{{\ \rm per\ cent}}$ of the power from supernovae, suggesting inefficient preventive CR feedback for the physical conditions modelled here. We predict significant spatially extended emission and absorption lines from 104–105.5 K gas; this may correspond to extraplanar diffuse ionized gas seen in star-forming galaxies.

Constraints on galaxy formation from the cosmic-far-infrared-background – optical-imaging cross-correlation using Herschel and UNIONS

ABSTRACT Using Herschel-SPIRE imaging and the Canada-France Imaging Survey (CFIS) Low Surface Brightness data products from the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS), we present a cross-correlation between the cosmic far-infrared background and cosmic optical background fluctuations. The cross-spectrum is measured for two cases: all galaxies are kept in the images; or all individually detected galaxies are masked to produce ‘background’ maps. We report the detection of the cross-correlation signal at $\gtrsim 18\, \sigma$ ($\gtrsim 14\, \sigma$ for the background map). The part of the optical brightness variations that are correlated with the submm emission translates to an rms brightness of $\simeq 32.5\, {\rm mag}\, {\rm arcsec}^{-2}$ in the r band, a level normally unreachable for individual sources. A critical issue is determining what fraction of the cross-power spectrum might be caused by emission from Galactic cirrus. For one of the fields, the Galactic contamination is 10 times higher than the extragalactic signal; however, for the other fields, the contamination is around 20 per cent. An additional discriminant is that the cross-power spectrum is of the approximate form P(k) ∝ 1/k, much shallower than that of Galactic cirrus. We interpret the results in a halo-model framework, which shows good agreement with independent measurements for the scalings of star-formation rates in galaxies. The approach presented in this study holds great promise for future surveys such as FYST/CCAT-prime combined with Euclid or the Vera Rubin Observatory (LSST), which will enable a detailed exploration of the evolution of star formation in galaxies.

Not hydro: using neural networks to estimate galaxy properties on a dark-matter-only simulation

ABSTRACT Using data from TNG300-2, we train a neural network (NN) to recreate the stellar mass (M*) and star formation rate (SFR) of central Galaxies in a dark-matter-only simulation. We conider 12 input properties from the halo and sub-halo hosting the galaxy and the near environment. M* predictions are robust, but the machine does not fully reproduce its scatter. The same happens for SFR, but the predictions are not as good as for M*. We chained NNs, improving the predictions on SFR to some extent. For SFR, we time-averaged this value between z = 0 and z = 0.1, which improved results for z = 0. Predictions of both variables have trouble reproducing values at lower and higher ends. We also study the impact of each input variable in the performance of the predictions using a leave-one-covariate-out approach, which led to insights about the physical and statistical relation between input variables. In terms of metrics, our machine outperforms similar studies, but the main discoveries in this work are not linked with the quality of the predictions themselves, but to how the predictions relate to the input variables. We find that previously studied relations between physical variables are meaningful to the machine. We also find that some merger tree properties strongly impact the performance of the machine. We conclude that machine learning models are useful tools to understand the significance of physical different properties and their impact on target characteristics, as well as strong candidates for potential simulation methods.

Probing bursty star formation by cross-correlating extragalactic background light and galaxy surveys

ABSTRACT Understanding the star formation rate (SFR) variability and how it depends on physical properties of galaxies is important for developing and testing the theory of galaxy formation. We investigate how statistical measurements of the extragalactic background light (EBL) can shed light on this topic and complement traditional methods based on observations of individual galaxies. Using semi-empirical models of galaxy evolution and SFR indicators sensitive to different star formation time-scales (e.g. H α and ultraviolet continuum luminosities), we show that the SFR variability, quantified by the joint probability distribution of the SFR indicators (i.e. the bivariate conditional luminosity function), can be characterized as a function of galaxy mass and redshift through the cross-correlation between deep, near-infrared maps of the EBL and galaxy distributions. As an example, we consider combining upcoming SPHEREx maps of the EBL with galaxy samples from Rubin Observatory Legacy Survey of Space and Time. We demonstrate that their cross-correlation over a sky fraction of fsky ∼ 0.5 can constrain the joint SFR indicator distribution at high significance up to z ∼ 2.5 for mass-complete samples of galaxies down to $M_{*}\sim 10^9\, {\rm M}_{\odot }$. These constraints not only allow models of different SFR variability to be distinguished, but also provide unique opportunities to investigate physical mechanisms that require large number statistics such as environmental effects. The cross-correlations investigated illustrate the power of combining cosmological surveys to extract information inaccessible from each data set alone, while the large galaxy populations probed capture ensemble-averaged properties beyond the reach of targeted observations towards individual galaxies.

Panchromatic Photometry of Low-redshift, Massive Galaxies Selected from SDSS Stripe 82

The broadband spectral energy distribution of a galaxy encodes valuable information on its stellar mass, star formation rate (SFR), dust content, and possible fractional energy contribution from nonstellar sources. We present a comprehensive catalog of panchromatic photometry, covering 17 bands from the far-ultraviolet to 500 μm, for 2685 low-redshift (z = 0.01–0.11), massive (M * > 1010 M ⊙) galaxies selected from the Stripe 82 region of the Sloan Digital Sky Survey, one of the largest areas with relatively deep, uniform observations over a wide range of wavelengths. Taking advantage of the deep optical coadded images, we develop a hybrid approach for matched-aperture photometry of the multiband data. We derive robust uncertainties and upper limits for undetected galaxies, deblend interacting/merging galaxies and sources in crowded regions, and treat contamination by foreground stars. We perform spectral energy distribution fitting to derive the stellar mass, SFR, and dust mass, critically assessing the influence of flux upper limits for undetected photometric bands and applying corrections for systematic uncertainties based on extensive mock tests. Comparison of our measurements with those of commonly used published catalogs reveals good agreement for the stellar masses. While the SFRs of galaxies on the star-forming main sequence show reasonable consistency, galaxies in and below the green valley show considerable disagreement between different sets of measurements. Our analysis suggests that one should incorporate the most accurate and inclusive photometry into the spectral energy distribution analysis, and that care should be exercised in interpreting the SFRs of galaxies with moderate to weak star formation activity.

An Updated Dust-to-Star Geometry: Dust Attenuation Does Not Depend on Inclination in 1.3 ≤z ≤2.6 Star-forming Galaxies from MOSDEF

We investigate dust attenuation and its dependence on viewing angle for 308 star-forming galaxies at 1.3 ≤ z ≤ 2.6 from the MOSFIRE Deep Evolution Field survey. We divide galaxies with a detected Hα emission line and coverage of Hβ into eight groups by stellar mass, star formation rate (SFR), and inclination (i.e., axis ratio), and we then stack their spectra. From each stack, we measure the Balmer decrement and gas-phase metallicity, and then we compute the median A V and UV continuum spectral slope (β). First, we find that none of the dust properties (Balmer decrement, A V, or β) varies with the axis ratio. Second, both stellar and nebular attenuation increase with increasing galaxy mass, showing little residual dependence on SFR or metallicity. Third, nebular emission is more attenuated than stellar emission, and this difference grows even larger at higher galaxy masses and SFRs. Based on these results, we propose a three-component dust model in which attenuation predominantly occurs in star-forming regions and large, dusty star-forming clumps, with minimal attenuation in the diffuse ISM. In this model, nebular attenuation primarily originates in clumps, while stellar attenuation is dominated by star-forming regions. Clumps become larger and more common with increasing galaxy mass, creating the above mass trends. Finally, we argue that a fixed metal yield naturally leads to mass regulating dust attenuation. Infall of low-metallicity gas increases the SFR and lowers the metallicity, but leaves the dust column density mostly unchanged. We quantify this idea using the Kennicutt–Schmidt and fundamental metallicity relations, showing that galaxy mass is indeed the primary driver of dust attenuation.

The relationship between the incidence of X-ray selected AGN in nearby galaxies &amp; star-formation rate

ABSTRACT We present the identification and analysis of an X-ray selected AGN sample that lie within the local (z &amp;lt; 0.35) galaxy population. From a parent sample of 22 079 MPA-JHU (based on SDSS DR8) galaxies, we identified 917 galaxies with central, excess X-ray emission (from 3XMM-DR7) likely originating from an AGN. We measured the host galaxies’ star formation rates and classified them as either star-forming or quiescent based on their position relative to main sequence of star formation. Only 72 per cent of the X-ray selected sample were identified as AGN using BPT selection; this technique is much less effective in quiescent hosts, only identifying 50 per cent of the X-ray AGN. We also calculated the growth rates of the black holes powering these AGN in terms of their specific accretion rate (∝ LX/M*) and found quiescent galaxies, on average, accrete at a lower rate than star-forming galaxies. Finally, we measured the sensitivity function of 3XMM so we could correct for observational bias and construct probability distributions as a function of accretion rate. AGN were found in galaxies across the full range of star formation rates ($\log _{10} \, \mathrm{SFR/M_\odot \ yr^{-1}} = -3\ \mathrm{to}\ 2$) in both star-forming and quiescent galaxies. The incidence of AGN was enhanced by a factor 2 (at a 3.5σ significance) in star-forming galaxies compared to quiescent galaxies of equivalent stellar mass and redshift, but we also found a significant population of AGN hosted by quiescent galaxies.

Star-formation-rate estimates from water emission

Context. The star-formation rate (SFR) quantitatively describes the star-formation process in galaxies throughout cosmic history. Current ways to calibrate this rate do not usually employ observational methods accounting for the low-mass end of stellar populations as their signatures are too weak. Aims. Accessing the bulk of protostellar activity within galactic star-forming regions can be achieved by tracing signposts of ongoing star formation. One such signpost is molecular outflows, which are particularly strong at the earliest stages of star formation. These outflows are bright in molecular emission, which is readily observable. We propose to utilize the protostellar outflow emission as a tracer of the SFR. Methods. In this work, we introduce a novel version of the galaxy-in-a-box model, which can be used to relate molecular emission from star formation in galaxies with the SFR. We measured the predicted para-water emission at 988 GHz (which is particularly bright in outflows) and corresponding SFRs for galaxies with LFIR = 108 − 1011 L⊙ in a distance-independent manner, and compared them with expectations from observations. Results. We evaluated the derived results by varying star-forming parameters, namely the star formation efficiency, the free-fall time scaling factor, and the initial mass function. We observe that for the chosen water transition, relying on the current Galactic observations and star formation properties, we are underestimating the total galactic emission, while overestimating the SFRs, particularly for more starburst-like configurations. Conclusions. The current version of the galaxy-in-a-box model only accounts for a limited number of processes and configurations, that is, it focuses on ongoing star formation in massive young clusters in a spiral galaxy. Therefore, the inferred results, which underestimate the emission and overestimate the SFR, are not surprising: known sources of emission are not included in the model. To improve the results, the next version of the model needs to include a more detailed treatment of the entire galactic ecosystem and other processes that would contribute to the emission. Thus, the galaxy-in-a-box model is a promising step toward unveiling the star-forming properties of galaxies across cosmic time.

The Young and the Wild: What Happens to Protoclusters Forming at Redshift z ≈ 4?

Using one of the largest volumes of the hydrodynamical cosmological simulation suit Magneticum, we study the evolution of protoclusters identified at redshift ≈ 4, with properties similar to the well-observed protocluster SPT2349-56. We identify 42 protoclusters in the simulation as massive and equally rich in substructures as observed, confirming that these observed structures can already be virialized. The dynamics of the internally fast-rotating member galaxies within these protoclusters resemble observations, merging rapidly to form the cores of the brightest cluster galaxies of the assembling clusters. Half of the gas reservoir of these structures is in a hot phase, with the metal enrichment at a very early stage. These systems show a good agreement with the observed amount of cold star-forming gas, largely enriched to solar values. We predict that some of the member galaxies are already quenched at z ≈ 4, rendering them undetectable through measurements of their gas reservoirs. Tracing the evolution of protoclusters reveals that none of the typical mass indicators at high redshift are good tracers to predict the present-day mass of the system. We find that none of the simulated protoclusters at z = 4.3 are among the top ten most massive clusters at redshift z = 0.2, with some barely reaching masses of M ≈ 2 × 1014 M ⊙. Although the average star formation and mass growth rates in the simulated galaxies match observations at high redshift reasonably well, the simulation fails to reproduce the extremely high total star formation rates within the observed protoclusters, indicating that the subgrid models are lacking the ability to reproduce a higher star formation efficiency (or lower depletion timescales).