arXiv subjects

A. Katsianis

Publications and source records attributed to A. Katsianis.

9 recordsLinked to original sources

arXiv2025

The observed total star formation rate function up to z \sim 6: complementary UV and IR contributions and comparison with state-of-the-art galaxy formation models

We investigate how the obscured IR-derived and the dust-corrected UV star formation rate functions (SFRFs) compare with each other, and with predictions from state-of-the-art theoretical models of galaxy formation and evolution. We derive the IR-SFRF from the ALMA A$^3$COSMOS survey, by converting the IR luminosity functions (IR-LFs) into SFRF after correcting for AGN contribution. Similarly, we obtain the UV SFRFs from literature UV LFs, corrected for dust-extinction. First, we fit the two SFRFs independently via a MCMC approach, then we combine them to obtain the first estimate of the total SFRF out to $z \sim 6$. Finally, we compare this SFRF with the predictions of a set of theoretical models. We derived the UV (dust-extinction corrected, from literature UV-LFs) and IR SFRFs (from Herschel and ALMA IR-LFs) at $0.5 < z < 6$ , finding that they are mostly complementary, covering different ranges in star formation rate (SFR$ < 10-100$ M$_{\odot}$yr$^{-1}$ for the UV-corrected and SFR$ > 100$ M$_{\odot}$yr$^{-1}$ for the IR). From the comparison of the total SFRF with model predictions we find an overall good agreement at $z < 2.5$, with increasing difference at higher redshifts, with all models missing the galaxies that are forming stars with the highest SFRs. We finally obtained the UV (dust-corrected), IR and total star formation rate densities (SFRDs), finding that there are no redshift ranges where UV and IR alone are able to reproduce the whole total SFRD.

astro-ph.GA↗

arXiv2024

Understanding the Universal Dust Attenuation Scaling Relation of Star-Forming Galaxies

Star-forming galaxies (SFGs) adhere to a surprisingly tight scaling relation of dust attenuation parameterized by the infrared excess (IRX=$L_{\rm IR}/L_{\rm UV}$), being jointly determined by the star formation rate (SFR), galaxy size ($R_{\rm e}$), metallicity ($Z$/Z$_\odot$) and axial ratio ($b/a$). We examine how these galaxy parameters determine the effective dust attenuation and give rise to the universal IRX relation, utilizing a simple two-component star-dust geometry model in which dust in the dense and diffuse interstellar medium (ISM) follows exponential mass density profiles, connected with but not necessarily identical to the stellar mass profiles. Meanwhile, empirical relations are adopted to link galaxy properties, including the gas--star formation relation, the dust-to-stellar size relation, as well as the dust-to-gas ratio versus metallicity relation. By fitting a large sample of local SFGs with the model, we obtain the best-fitting model parameters as a function of metallicity, showing that the two-component geometry model is able to successfully reproduce the dependence of IRX on SFR, $R_{\rm e}$, $b/a$ at given $Z$/Z$_\odot$, as well as the dependence of power-law indices on metallicity. Moreover, we also retrieve constraints on the model geometry parameters, including the optical depth of birth clouds (BCs), BC-to-total dust mass fraction, BC covering factor of UV-emitting stars, and star-to-total dust disc radius ratio, which all evolve with galaxy metallicity. Finally, a consistent picture of how the star-dust geometry in SFGs evolves with galaxy metallicity is discussed.

astro-ph.GA↗

arXiv2022

Orientation effects on cool gas absorption from gravitational-arc tomography of a z = 0.77 disc galaxy

We use spatially-resolved spectroscopy of a distant giant gravitational arc to test orientation effects on MgII absorption equivalent width (EW) and covering fraction (kappa) in the circumgalactic medium of a foreground star-forming galaxy (G1) at z~0.77. Forty-two spatially-binned arc positions uniformly sample impact parameters (D) to G1 between 10 and 30 kpc and azimuthal angles alpha between 30 and 90 degrees (minor axis). We find an EW-D anti-correlation, akin to that observed statistically in quasar absorber studies, and an apparent correlation of both EW and kappa with alpha, revealing a non-isotropic gas distribution. In line with our previous results on MgII kinematics suggesting the presence of outflows in G1, at minimum a simple 3-D static double-cone model (to represent the trace of bipolar outflows) is required to recreate the EW spatial distribution. The D and alpha values probed by the arc cannot confirm the presence of a disc, but the data highly disfavor a disc alone. Our results support the interpretation that the EW-alpha correlation observed statistically using other extant probes is partly shaped by bipolar metal-rich winds.

astro-ph.GA↗

arXiv2021

Telltale signs of metal recycling in the circumgalactic medium of a $z \sim 0.77$ galaxy

We present gravitational-arc tomography of the cool-warm enriched circumgalactic medium (CGM) of an isolated galaxy (``G1'') at $z \approx 0.77$. Combining VLT/MUSE adaptive-optics and Magellan/MagE echelle spectroscopy we obtain partially-resolved kinematics of MgII in absorption and [OII] in emission. The unique arc configuration allows us to probe 42 spatially independent arc positions transverse to G1, plus 4 positions in front of it. The transverse positions cover G1's minor and major axes at impact parameters of $\approx 10-30$ kpc and $\approx 60$ kpc, respectively. We observe a direct kinematic connection between the cool-warm enriched CGM (traced by MgII) and the interstellar medium (traced by [OII]). This provides strong evidence for the existence of an extended disc that co-rotates with the galaxy out to tens of kiloparsecs. The MgII velocity dispersion ($σ\approx 30-100$ km s$^{-1}$, depending on position) is of the same order as the modeled galaxy rotational velocity ($v_{\rm rot} \approx 80$ km s$^{-1}$), providing evidence for the presence of a turbulent and pressure-supported CGM component. We regard the absorption to be modulated by a galactic-scale outflow, as it offers a natural scenario for the observed line-of-sight dispersion and asymmetric profiles observed against both the arcs and the galaxy. An extended enriched co-rotating disc together with the signatures of a galactic outflow, are telltale signs of metal recycling in the $z\sim 1$ CGM.

astro-ph.GA↗

arXiv2020

The high redshift SFR-M* relation is sensitive to the employed star formation rate and stellar mass indicators: Towards addressing the tension between observations and simulations

There is a severe tension between the observed star formation rate (SFR) - stellar mass (${\rm M}_{\star}$) relations reported by different authors at $z = 1-4$. In addition, the observations have not been successfully reproduced by state-of-the-art cosmological simulations which tend to predict a factor of 2-4 smaller SFRs at a fixed ${\rm M}_{\star}$. We examine the evolution of the SFR$-{\rm M}_{\star}$ relation of $z = 1-4 $ galaxies using the SKIRT simulated spectral energy distributions of galaxies sampled from the EAGLE simulations. We derive SFRs and stellar masses by mimicking different observational techniques. We find that the tension between observed and simulated SFR$-{\rm M}_{\star}$ relations is largely alleviated if similar methods are used to infer the galaxy properties. We find that relations relying on infrared wavelengths (e.g. 24 ${\rm μm}$, MIPS - 24, 70 and 160 ${\rm μm}$ or SPIRE - 250, 350, 500 ${\rm μm}$) have SFRs that exceed the intrinsic relation by 0.5 dex. Relations that rely on the spectral energy distribution fitting technique underpredict the SFRs at a fixed stellar mass by -0.5 dex at $z \sim 4$ but overpredict the measurements by 0.3 dex at $z \sim 1$. Relations relying on dust-corrected rest-frame UV luminosities, are flatter since they overpredict/underpredict SFRs for low/high star forming objects and yield deviations from the intrinsic relation from 0.10 dex to -0.13 dex at $z \sim 4$. We suggest that the severe tension between different observational studies can be broadly explained by the fact that different groups employ different techniques to infer their SFRs.

astro-ph.GA↗

arXiv2019

Slicing the cool circumgalactic medium along the major-axis of a star-forming galaxy at $z = 0.7$

We present spatially-resolved echelle spectroscopy of an intervening MgII-FeII-MgI absorption-line system detected at $z_{\rm abs}=0.73379$ toward the giant gravitational arc PSZ1 G311.65-18.48. The absorbing gas is associated to an inclined disk-like star-forming galaxy, whose major axis is aligned with the two arc-segments reported here. We probe in absorption the galaxy's extended disk continuously, at $\approx 3$ kpc sampling, from its inner region out to $15\times$ the optical radius. We detect strong ($W_0^{2796}>0.3$ Å) coherent absorption along $13$ independent positions at impact parameters $D=0$--$29$ kpc on one side of the galaxy, and no absorption at $D=28$--$57$ kpc on the opposite side (all de-lensed distances at $z_{\rm abs}$). We show that: (1) the gas distribution is anisotropic; (2) $W_0^{2796}$, $W_0^{2600}$, $W_0^{2852}$, and the ratio $W_0^{2600}\!/W_0^{2796}$, all anti-correlate with $D$; (3) the $W_0^{2796}$-$D$ relation is not cuspy and exhibits significantly less scatter than the quasar-absorber statistics; (4) the absorbing gas is co-rotating with the galaxy out to $D \lesssim 20$ kpc, resembling a `flat' rotation curve, but at $D\gtrsim 20$ kpc velocities decline below the expectations from a 3D disk-model extrapolated from the nebular [OII] emission. These signatures constitute unambiguous evidence for rotating extra-planar diffuse gas, possibly also undergoing enriched accretion at its edge. Arguably, we are witnessing some of the long-sought processes of the baryon cycle in a single distant galaxy expected to be representative of such phenomena.

astro-ph.GA↗

arXiv2018

Galaxy And Mass Assembly (GAMA): The sSFR-M* relation part I - $σ_{\mathrm{sSFR}}$-M* as a function of sample, SFR indicator and environment

Recently a number of studies have proposed that the dispersion along the star formation rate - stellar mass relation ($σ_{\mathrm{sSFR}}$-M$_{*}$) is indicative of variations in star-formation history (SFH) driven by feedback processes. They found a 'U'-shaped dispersion and attribute the increased scatter at low and high stellar masses to stellar and active galactic nuclei feed-back respectively. However, measuring $σ_{\mathrm{sSFR}}$ and the shape of the $σ_{\mathrm{sSFR}}$-M$_{*}$ relation is problematic and can vary dramatically depending on the sample selected, chosen separation of passive/star-forming systems, and method of deriving star-formation rates ($i.e.$ H$α$ emission vs spectral energy distribution fitting). As such, any astrophysical conclusions drawn from measurements of $σ_{\mathrm{sSFR}}$ must consider these dependencies. Here we use the Galaxy And Mass Assembly survey to explore how $σ_{\mathrm{sSFR}}$ varies with SFR indicator for a variety of selections for disc-like `main sequence' star-forming galaxies including colour, star-formation rate, visual morphology, bulge-to-total mass ratio, Sérsic index and mixture modelling. We find that irrespective of sample selection and/or SFR indicator, the dispersion along the sSFR-M$_{*}$ relation does follow a 'U'-shaped distribution. This suggests that the shape is physical and not an artefact of sample selection or method. We then compare the $σ_{\mathrm{sSFR}}$-M$_{*}$ relation to state-of-the-art hydrodynamical and semi-analytic models and find good agreement with our observed results. Finally, we find that for group satellites this 'U'-shaped distribution is not observed due to additional high scatter populations at intermediate stellar masses.

astro-ph.GA↗

arXiv2017

The evolution of the star formation rate function in the EAGLE simulations: A comparison with UV, IR and H$α$ observations from z ~ 8 to z ~ 0

We investigate the evolution of the galaxy Star Formation Rate Function (SFRF) and Cosmic Star Formation Rate Density (CSFRD) of $z\sim 0-8 $ galaxies in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations. In addition, we present a compilation of UV, IR and H$α$ SFRFs and compare these with the predictions from the EAGLE suite of cosmological hydrodynamic simulations. We find that the constraints implied by different indicators are inconsistent with each other for the highest star-forming objects at z < 2, a problem that is possibly related to selection biases and the uncertainties of dust attenuation effects. EAGLE's feedback parameters were calibrated to reproduce realistic galaxy sizes and stellar masses at z = 0.1. In this work we test if and why those choices yield realistic Star Formation Rates (SFRs) for $z \sim 0-8$ as well. We demonstrate that SNe feedback plays a major role at setting the abundance of galaxies at all star-forming regimes, especially at high redshifts. On the contrary, Active Galactic Nuclei (AGN) feedback becomes more prominent at lower redshifts and is a major mechanism that affects only the highest star-forming systems. Furthermore, we find that galaxies with SFR $\sim 1-10 \, {\rm M_{\odot} \, yr^{-1}}$ dominate the CSFRD at redshifts z < 5, while rare high star-forming galaxies (SFR $\sim 10-100 \,{\rm M_{\odot} \, yr^{-1}}$) contribute significantly only briefly around the peak era ($z \sim 2$) and then are quenched by AGN feedback. In the absence of this prescription objects with SFR $\sim 10-100 \,{\rm M_{\odot} \, yr^{-1}}$ would dominate the CSFRD, while the cosmic budget of star formation would be extremely high. Finally, we demonstrate that the majority of the cosmic star formation occurs in relatively rare high mass halos ($ {\rm M_{Halo}} \sim 10^{11-13} \, {\rm M_{\odot}}$) even at the earliest epochs.

astro-ph.GA↗

arXiv2016

The relation between star formation rate and stellar mass of galaxies at z $\sim$ 1-4

The relation between the Star Formation Rate (SFR) and stellar mass (${\rm M}_{\star}$) of galaxies represents a fundamental constraint on galaxy formation and has been studied extensively both in observations and cosmological simulations. However, the observed amplitude has not been successfully reproduced in simulations, indicating either that the halo accretion history and baryonic physics are poorly modeled or that observations contain biases. We examine the evolution of the SFR$-{\rm M}_{\star}$ relation of $z\sim1-4 $ galaxies and display the inconsistency between observed relations that are obtained using different techniques. We employ cosmological hydrodynamic simulations and compare these with a range of observed SFR$-{\rm M}_{\star}$ relations. We find that numerical results are consistent with observations that use Spectral Energy Distribution (SED) techniques to estimate star formation rates and dust corrections. On the contrary, simulations are not able to reproduce results that were obtained by combining only UV and IR luminosities. These imply SFRs at a fixed stellar mass that are larger almost by a factor of 5 than those of SED measurements for $z \sim1.5-4$. Furthermore, we find remarkable agreement between the numerical results from various authors who have employed different cosmological codes and run simulations with different resolutions. This is interesting for two reasons. A) simulations can produce realistic populations of galaxies within representative cosmological volumes even at relatively modest resolutions. B) It is likely that current numerical codes that rely on similar subgrid multiphase Inter-Stellar Medium (ISM) models and are tuned to reproduce statistical properties of galaxies, produce similar results for the SFR$-{\rm M}_{\star}$ relation by construction, regardless of resolution, box size and, to some extent, the adopted feedback prescriptions.

astro-ph.GA↗