Similar Specific Star Formation Rates Research Articles

MOSEL survey: Unwrapping the Epoch of Reionization through mimic galaxies at Cosmic Noon

Abstract The nature of the first galaxies that reionized the universe during the Epoch of Reionization (EoR) remains unclear. Attempts to directly determine spectral properties of these early galaxies are affected by both limited photometric constraints across the spectrum and by the opacity of the intergalactic medium (IGM) to the Lyman Continuum (LyC) at high redshift. We approach this by analysing properties of analogous extreme emission line galaxies (EELGs, [OIII]+Hbeta EW> 400) at 2.5 < z < 4 from the ZFOURGE survey using the Multi-wavelength Analysis of Galaxy Physical Properties (MAGPHYS) SED fitting code. We compare these to galaxies at z > 5.5 observed with the James Webb Space Telesope (JWST) with self-consistent spectral energy distribution fitting methodology. This work focuses on the comparison of their UV slopes (βP), ionizing photon production efficiencies ξion, star formation rates and dust properties to determine the effectiveness of this analogue selection technique. We report the median ionizing photon production efficiencies as for our ZFOURGE control, ZFOURGE EELG, JADES and CEERS samples respectively. ZFOURGE EELGs are 0.57 dex lower in stellar mass and have half the dust extinction, compared to their ZFOURGE control counterparts. They also have a similar specific star formation rates and βP to the z > 5.5 samples. We find that EELGs at low redshift (2.5 < z < 4) are analogous to EoR galaxies in their dust attenuation and specific star formation rates. Their extensive photometric coverage and the accessibility of their LyC region opens pathways to infer stellar population properties in the EoR.

HETDEX [O iii] Emitters. I. A Spectroscopically Selected Low-redshift Population of Low-mass, Low-metallicity Galaxies

Abstract We assemble a sample of 17 low-metallicity (7.45 < log(O/H)+12 < 8.12) galaxies with z ≲ 0.1 found spectroscopically, without photometric preselection, in early data from the Hobby–Eberly Telescope Dark Energy Experiment. Star-forming galaxies that occupy the lowest-mass and lowest-metallicity end of the mass–metallicity relation tend to be undersampled in continuum-based surveys as their spectra are typically dominated by emission from newly forming stars. We search for galaxies with high [O iii]λ5007/[O ii]λ3727, implying highly ionized nebular emission often indicative of low-metallicity systems. With the Second Generation Low Resolution Spectrograph on the Hobby–Eberly Telescope we acquired follow-up spectra, with higher resolution and broader wavelength coverage, of each low-metallicity candidate in order to confirm the redshift, measure the Hα and [N ii] line strengths, and, in many cases, obtain deeper spectra of the blue lines. We find our galaxies are consistent with the mass–metallicity relation of typical low-mass galaxies. However, galaxies in our sample tend to have similar specific star formation rates as the incredibly rare “blueberry” galaxies found by Yang et al. We illustrate the power of spectroscopic surveys for finding low-mass and low-metallicity galaxies and reveal that we find a sample of galaxies that are a hybrid between the properties of typical dwarf galaxies and the more extreme blueberry galaxies.

The Activation of Galactic Nuclei and Their Accretion Rates Are Linked to the Star Formation Rates and Bulge-types of Their Host Galaxies

Abstract We use bulge-type classifications of 809 representative Sloan Digital Sky Survey galaxies by Gadotti to classify a large sample of galaxies into real bulges (classical or elliptical) and pseudobulges using Random Forest. We use structural and stellar population predictors that can easily be measured without image decomposition. Multiple parameters—such as the central-mass density with 1 kpc, concentration index, Sérsic index, and velocity dispersion—result in accurate bulge classifications when combined together. We classify ∼44,500 face-on galaxies above stellar mass of 1010 M ⊙ and redshift 0.02 < z < 0.07 into real bulges or pseudobulges with 93% ± 2% accuracy. We show that ∼75%–90% of active galactic nuclei (AGNs) identified by the optical line ratio diagnostic are hosted by real bulges. The pseudobulge fraction significantly decreases with AGN signature as the line ratios change from indicating pure star formation (∼54% ± 4%), to composite of star formation and AGN (∼18% ± 3%), and to AGN-dominated galaxies (∼5% ± 3%). Using the dust-corrected [O iii] luminosity as an AGN accretion indicator, and the stellar mass and radius as proxies for a black hole mass, we find that AGNs in real bulges have lower Eddington ratios than AGNs in pseudobulges. Real bulges have a wide range of AGN and star formation activities, although most of them are weak AGNs. For both bulge-types, their Eddington ratios are correlated with specific star formation rates (SSFR). Real bulges have a lower specific accretion rate but higher AGN fraction than pseudobulges do at similar SSFRs.

The Origin of Faint Tidal Features around Galaxies in the RESOLVE Survey

Abstract We study tidal features around galaxies in the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey. Our sample consists of 1048 RESOLVE galaxies that overlap with the DECam Legacy Survey, which reaches an r-band 3σ depth of ∼27.9 mag arcsec−2 for a 100 arcsec2 feature. Images were masked, smoothed, and inspected for tidal features such as streams, shells, or tails/arms. We find tidal features in 17±2% of our galaxies, setting a lower limit on the true frequency. The frequency of tidal features in the gas-poor (gas-to-stellar mass ratio <0.1) subsample is lower than in the gas-rich subsample (13±3% versus 19±2%). Within the gas-poor subsample, galaxies with tidal features have higher stellar and halo masses, ∼3× closer distances to nearest neighbors (in the same group), and possibly fewer group members at fixed halo mass than galaxies without tidal features, but similar specific star formation rates. These results suggest tidal features in gas-poor galaxies are typically streams/shells from dry mergers or satellite disruption. In contrast, the presence of tidal features around gas-rich galaxies does not correlate with stellar or halo mass, suggesting these tidal features are often tails/arms from resonant interactions. Similar to tidal features in gas-poor galaxies, tidal features in gas-rich galaxies imply 1.7× closer nearest neighbors in the same group; however, they are associated with diskier morphologies, higher star formation rates, and higher gas content. In addition to interactions with known neighbors, we suggest that tidal features in gas-rich galaxies may arise from accretion of cosmic gas and/or gas-rich satellites below the survey limit.

Linking the structural properties of galaxies and their star formation histories with STAGES

We study the links between star formation history and structure for a large mass-selected galaxy sample at 0.05 < z_phot < 0.30. The galaxies inhabit a very broad range of environments, from cluster cores to the field. Using HST images, we quantify their structure following Hoyos et al. (2012), and divide them into disturbed and undisturbed. We also visually identify mergers. Additionally, we provide a quantitative measure of the degree of disturbance for each galaxy ("roughness"). The majority of elliptical and lenticular galaxies have relaxed structure, showing no signs of ongoing star formation. Structurally-disturbed galaxies, which tend to avoid the lowest-density regions, have higher star-formation activity and younger stellar populations than undisturbed systems. Cluster spirals with reduced/quenched star formation have somewhat less disturbed morphologies than spirals with "normal" star-formation activity, suggesting that these "passive" spirals have started their morphological transformation into S0s. Visually identified mergers and galaxies not identified as mergers but with similar roughness have similar specific star formation rates and stellar ages. The degree of enhanced star formation is thus linked to the degree of structural disturbance, regardless of whether it is caused by major mergers or not. This suggests that merging galaxies are not special in terms of their higher-than-normal star-formation activity. Any physical process that produces "roughness", or regions of enhanced luminosity density, will increase the star-formation activity in a galaxy with similar efficiency. An alternative explanation is that star formation episodes increase the galaxies' roughness similarly, regardless of whether they are merger-induced or not.

STAR FORMATION IN THE CENTRAL REGIONS OF ACTIVE AND NORMAL GALAXIES

We investigated the properties of the host galaxies of active galactic nuclei (AGNs). We used radio emission around the nuclei of the host galaxies to represent AGN activity and used infrared (IR) emission to represent the star-forming activity and stellar population of the host galaxies. We determined that active galaxies have higher stellar masses (SMs) within the central kiloparsec radius than normal galaxies do independent of the Hubble types of the host galaxies; but both active and normal galaxies exhibit similar specific star formation rates (SSFRs), ranging between and yr−1. We find that the central SM surface density might be used as an indicator to identify AGNs. We also discovered that certain AGNs exhibit substantial inner stellar structures in the IR images; most of the AGNs with inner structures are Seyferts, whereas only a few LINERs exhibit inner structures. We note that the AGNs with inner structures show a positive correlation between the radio activity of the AGNs and the SFRs of the host galaxies, but the sources without inner structures show a negative correlation between the radio power and the SFRs. These results might be explained with a scenario of starburst–AGN evolution. In this scenario, AGN activities are triggered following a nuclear starburst; during the evolution, AGN activities are accompanied by SF activity in the inner regions of the host galaxies; at the final stage of the evolution, the AGNs might transform into LINERs, exhibiting weak SF activity in the central regions of the host galaxies.

THE AROMATIC FEATURES IN VERY FAINT DWARF GALAXIES

We present optical and mid-infrared photometry of a statistically complete sample of 29 very faint dwarf galaxies (M_r > -15 mag) selected from the SDSS spectroscopic sample and observed in the mid-infrared with Spitzer IRAC. This sample contains nearby (redshift z<0.005) galaxies three magnitudes fainter than previously studied samples. We compare our sample with other star-forming galaxies that have been observed with both IRAC and SDSS. We examine the relationship of the infrared color, sensitive to PAH abundance, with star-formation rates, gas-phase metallicities and radiation hardness, all estimated from optical emission lines. Consistent with studies of more luminous dwarfs, we find that the very faint dwarf galaxies show much weaker PAH emission than more luminous galaxies with similar specific star-formation rates. Unlike more luminous galaxies, we find that the very faint dwarf galaxies show no significant dependence at all of PAH emission on star-formation rate, metallicity, or radiation hardness, despite the fact that the sample spans a significant range in all of these quantities. When the very faint dwarfs in our sample are compared with more luminous (M_r ~ -18 mag) dwarfs, we find that PAH emission depends on metallicity and radiation hardness. These two parameters are correlated; we look at the PAH-metallicity relation at fixed radiation hardness and the PAH-hardness relation at fixed metallicity. This test shows that the PAH emission in dwarf galaxies depends most directly on metallicity.

The infrared emission of ultraviolet-selected galaxies fromz= 0 toz= 1

We select galaxies in UV rest-frame at z=0, z~0.7 and z~1 together with a sample of LBGs at z~1, the samples are built in order to sample the same range of luminosity at any redshift. The evolution of the IR and UV luminosities with z is analysed for individual galaxies as well as in terms of luminosity functions. The L_IR/L_UV ratio is used to measure dust attenuation. This ratio does not exhibit a strong evolution with z for the bulk of our sample galaxies but some trends are found for galaxies with a strong dust attenuation and for UV luminous sources: galaxies with L_IR/L_UV>10 are more frequent at z>0 than at z=0 and the largest values of L_IR/L_UV are found for UV faint objects; conversely the most luminous galaxies of our samples (L_UV> 2 10^{10} L_sun$), detected at z=1, exhibit a lower dust attenuation than the fainter ones. L_IR/L_UV increases with the K rest-frame luminosity of the galaxies at all the redshifts considered and shows a residual anti-correlation with L_UV. The most massive and UV luminous galaxies exhibit quite large specific star formation rates. LBGs exhibit systematically lower dust attenuation than UV selected galaxies of same luminosity but similar specific star formation rates. The analysis of the UV+IR luminosity functions leads to the conclusion that up to z = 1 most of the star formation activity of UV selected galaxies is emitted in IR. Whereas we are able to retrieve all the star formation from our UV selection at z=0.7, at z = 1 we miss a large fraction of galaxies more luminous than ~ 10^{11} L_sun. The effect is found larger for Lyman Break Galaxies.