We present new H$alpha$ photometry for the Star-Formation Reference Survey (SFRS), a representative sample of star-forming galaxies in the local Universe. Combining these data with the panchromatic coverage of the SFRS, we provide calibrations of H$a
lpha$-based star-formation rates (SFRs) with and without correction for the contribution of [$rm N_{^{II}}$] emission. We consider the effect of extinction corrections based on the Balmer decrement, infrared excess (IRX), and spectral energy distribution (SED) fits. We compare the SFR estimates derived from SED fits, polycyclic aromatic hydrocarbons, hybrid indicators such as 24 $mu$m + H$alpha$, 8 $mu$m + H$alpha$, FIR + FUV, and H$alpha$ emission for a sample of purely star-forming galaxies. We provide a new calibration for 1.4 GHz-based SFRs by comparing to the H$alpha$ emission, and we measure a dependence of the radio-to-H$alpha$ emission ratio based on galaxy stellar mass. Active galactic nuclei introduce biases in the calibrations of different SFR indicators but have only a minimal effect on the inferred SFR densities from galaxy surveys. Finally, we quantify the correlation between galaxy metallicity and extinction.
We constrain the mass distribution in nearby, star-forming galaxies with the Star Formation Reference Survey (SFRS), a galaxy sample constructed to be representative of all known combinations of star formation rate (SFR), dust temperature, and specif
ic star formation rate (sSFR) that exist in the Local Universe. An innovative two-dimensional bulge/disk decomposition of the 2MASS/$K_{s}$-band images of the SFRS galaxies yields global luminosity and stellar mass functions, along with separate mass functions for their bulges and disks. These accurate mass functions cover the full range from dwarf galaxies to large spirals, and are representative of star-forming galaxies selected based on their infra-red luminosity, unbiased by AGN content and environment. We measure an integrated luminosity density $j$ = 1.72 $pm$ 0.93 $times$ 10$^{9}$ L$_{odot}$ $h^{-1}$ Mpc$^{-3}$ and a total stellar mass density $rho_{M}$ = 4.61 $pm$ 2.40 $times$ 10$^{8}$ M$_{odot}$ $h^{-1}$ Mpc$^{-3}$. While the stellar mass of the emph{average} star-forming galaxy is equally distributed between its sub-components, disks globally dominate the mass density budget by a ratio 4:1 with respect to bulges. In particular, our functions suggest that recent star formation happened primarily in massive systems, where they have yielded a disk stellar mass density larger than that of bulges by more than 1 dex. Our results constitute a reference benchmark for models addressing the assembly of stellar mass on the bulges and disks of local ($z = 0$) star-forming galaxies.
We present the Heraklion Extragalactic Catalogue, or HECATE, an all-sky value-added galaxy catalogue, aiming to facilitate present and future multi-wavelength and multi-messenger studies in the local Universe. It contains 204,733 galaxies up to a red
shift of 0.047 (D<200 Mpc), and it is >50% complete in terms of the B-band luminosity density at distances in the 0-170 Mpc range. By incorporating and homogenising data from astronomical databases and multi-wavelength surveys, the catalogue offers positions, sizes, distances, morphological classifications, star-formation rates, stellar masses, metallicities, and nuclear activity classifications. This wealth of information can enable a wide-range of applications, such as: (i) demographic studies of extragalactic sources, (ii) initial characterisation of transient events, and (iii) searches for electromagnetic counterparts of gravitational-wave events. The catalogue is publicly available to the community at a dedicated portal, which will also host future extensions in terms of the covered volume, and data products.
We present a systematic study of the metallicity variations within the collisional ring galaxy NGC 922 based on long-slit optical spectroscopic observations. We find a metallicity difference between star-forming regions in the bulge and the ring, wit
h metallicities ranging from almost solar to significantly sub-solar ($rm{[12+log(O/H)]sim 8.2}$). We detect $rm He,_I$ emission in the bulge and the ring star-forming regions indicating ionization from massive stars associated with recent ($<10$ Myr) star-formation, in agreement with the presence of very young star-clusters in all studied regions. We find an anti-correlation between the X-ray luminosity and metallicity of the sub-galactic regions of NGC 922. The different regions have similar stellar population ages leaving metallicity as the main driver of the anti-correlation. The dependence of the X-ray emission of the different regions in NGC 922 on metallicity is in agreement with similar studies of the integrated X-ray output of galaxies and predictions from X-ray binary population models.
Using 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 sm
aller than 40,Mpc. The foreground/background contamination is ${sim}20%$. The ULX populations in bona-fide star-forming galaxies scale on average with star-formation rate (SFR) and stellar mass ($M_star$) such that the number of ULXs per galaxy is $0.45^{+0.06}_{-0.09}timesfrac{rm SFR}{rm M_odot,yr^{-1}}{+}3.3^{+3.8}_{-3.2}timesfrac{M_star}{rm M_odot}$. The scaling depends strongly on the morphological type. This analysis shows that early spiral galaxies contain an additional population of ULXs that scales with $M_star$. We also confirm the strong anti-correlation of the ULX rate with the host galaxys metallicity. In the case of early-type galaxies we find that there is a non-linear dependence of the number of ULXs with $M_star$, 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.
X-ray luminosity ($L_X$) originating from high-mass X-ray binaries (HMXBs) is tightly correlated with the host galaxys star-formation rate (SFR). We explore this connection at sub-galactic scales spanning ${sim}$7 dex in SFR and ${sim}$8 dex in speci
fic SFR (sSFR). There is good agreement with established relations down to ${rm SFR {simeq} 10^{-3},M_odot , yr^{-1}}$, below which an excess of X-ray luminosity emerges. This excess likely arises from low mass X-ray binaries. The intrinsic scatter of the $L_X$-SFR relation is constant, not correlated with SFR. Different star formation indicators scale with $L_X$ in different ways, and we attribute the differences to the effect of star formation history. The SFR derived from H$alpha$ shows the tightest correlation with X-ray luminosity because H$alpha$ emission probes stellar populations with ages similar to HMXB formation timescales, but the H$alpha$-based SFR is reliable only for $rm sSFR{>}10^{-12},M_odot , yr^{-1}/M_odot$.
We have compiled the most complete census of High-Mass X-ray Binaries (HMXBs) in the Small Magellanic Cloud with the aim to investigate the formation efficiency of young accreting binaries in its low metallicity environment. In total, we use 127 X-ra
y sources with detections in our chandra X-ray Visionary Program (XVP), supplemented by 14 additional (likely and confirmed) HMXBs identified by cite{2016A&A...586A..81H} that fall within the XVP area, but are not either detected in our survey (9 sources) or matched with any XVP source that has at least one OB counterpart in the OGLE-III catalog (5 sources). Specifically, we examine the number ratio of the HMXBs [N(HMXBs)] to {it (a)} the number of OB stars, {it (b)} the local star-formation rate (SFR), and {it (c)} the stellar mass produced during the specific star-formation burst, all as a function of the age of their parent stellar populations. Each of these indicators serves a different role, but in all cases we find that the HMXB formation efficiency increases as a function of time (following a burst of star formation) up to $sim$40--60,Myr, and then gradually decreases. The peak formation efficiency N(HMXB)/SFR is (49 $pm$ 14) $[10^{-5}~{rm M_{odot}/yr}]^{-1}$, in good agreement with previous estimates of the average formation efficiency in the broad $sim$20--60,Myr age range. The frequency of HMXBs is a factor of 8$times$ higher than at $sim$10,Myr, and 4$times$ higher than at $sim$260,Myr, i.e. at earlier and later epochs, respectively.
We present the results of a pair of 100 ksec Chandra observations in the Small Magellanic Cloud to survey high mass X-ray binaries (HMXBs), stars and LMXBs/CVs down to Lx = 4.3 x 10^32 erg/s The two SMC Deep Fields are located in the most active star
forming region of the bar, with Deep Field-1 positioned at the most pulsar-rich location identified from previous surveys. Two new pulsars were discovered in outburst: CXOU J004929.7-731058 (P=892s), CXOU J005252.2-721715 (P=326s), and 3 new HMXB candidates were identified. Of 15 Be-pulsars now known in the field, 13 were detected, with pulsations seen in 9 of them. Ephemerides demonstrate that 6 of the 10 pulsars known to exhibit regular outbursts were seen outside their periastron phase, and quiescent X-ray emission at Lx=10^33 - 10^34 is shown to be common. Comparison with ROSAT, ASCA, XMM-Newton catalogs resulted in positive identification of several previously ambiguous sources. Bright optical counterparts exist for 40 of the X-ray sources, of which 33 are consistent with early-type stars Mv<-2, B-V<0.2), and are the subject of a companion paper. The results point to an underlying HMXB population-density up to double that of active systems. The full catalog of 394 point-sources is presented along with detailed analyses of timing and spectral properties.
We perform aperture photometry and profile fitting on 419 globular cluster (GC) candidates with mV leq 23 mag identified in Hubble Space Telescope Advanced Camera for Surveys BVI imaging, and estimate the effective radii of the clusters. We identify
85 previously known spectroscopically-confirmed clusters, and newly identify 136 objects as good cluster candidates within the 3{sigma} color and size ranges defined by the spectroscopically confirmed clusters, yielding a total of 221 probable GCs. The luminosity function peak for the 221 probable GCs with estimated total dereddening applied is V ~(20.26 pm 0.13) mag, corresponding to a distance of ~3.7pm0.3 Mpc. The blue and red GC candidates, and the metal-rich (MR) and metal-poor (MP) spectroscopically confirmed clusters, are similar in half-light radius, respectively. Red confirmed clusters are about 6% larger in median half-light radius than blue confirmed clusters, and red and blue good GC candidates are nearly identical in half-light radius. The total population of confirmed and good candidates shows an increase in half-light radius as a function of galactocentric distance.
We present the most likely optical counterparts of 113 X-ray sources detected in our Chandra survey of the central region of the Small Magellanic Cloud (SMC) based on the OGLE-II and MCPS catalogs. We estimate that the foreground contamination and ch
ance coincidence probability are minimal for the bright optical counterparts (corresponding to OB type stars; 35 in total). We propose here for the first time 13 High-Mass X-ray Binaries (HMXBs), of which 4 are Be/X-ray binaries (Be-XRBs), and we confirm the previous classification of 18 Be-XRBs. We estimate that the new candidate Be-XRBs have an age of 15-85 Myr, consistent with the age of Be stars. We also examine the overabundance of Be-XRBs in the SMC fields covered by Chandra, in comparison with the Galaxy. In luminosities down to about 10^{34} erg/s, we find that SMC Be-XRBs are 1.5 times more common when compared to the Milky Way even after taking into account the difference in the formation rates of OB stars. This residual excess can be attributed to the lower metallicity of the SMC. Finally, we find that the mixing of Be-XRBs with other than their natal stellar population is not an issue in our comparisons of Be-XRBs and stellar populations in the SMC. Instead, we find indication for variation of the SMC XRB populations on kiloparsec scales, related to local variations of the formation rate of OB stars and slight variation of their age, which results in different relative numbers of Be stars and therefore XRBs.
