arXiv subjects

S. Heinis

Publications and source records attributed to S. Heinis.

41 records · Page 3Linked to original sources

arXiv2011

HerMES: detection of cosmic magnification of sub-mm galaxies using angular cross-correlation

Cosmic magnification is due to the weak gravitational lensing of sources in the distant Universe by foreground large-scale structure leading to coherent changes in the observed number density of the background sources. Depending on the slope of the background source number counts, cosmic magnification causes a correlation between the background and foreground galaxies, which is unexpected in the absence of lensing if the two populations are spatially disjoint. Previous attempts using submillimetre (sub-mm) sources have been hampered by small number statistics. The large number of sources detected in the {\it Herschel} Multi-tiered Extra-galactic Survey (HerMES) Lockman-SWIRE field enables us to carry out the first robust study of the cross-correlation between sub-mm sources and sources at lower redshifts. Using ancillary data we compile two low-redshift samples from SDSS and SWIRE with ~ 0.2 and 0.4, respectively, and cross-correlate with two sub-mm samples based on flux density and colour criteria, selecting galaxies preferentially at z ~ 2. We detect cross-correlation on angular scales between ~1 and 50 arcmin and find clear evidence that this is primarily due to cosmic magnification. A small, but non-negligible signal from intrinsic clustering is likely to be present due to the tails of the redshift distribution of the sub-mm sources overlapping with those of the foreground samples.

astro-ph.CO↗

arXiv2010

Measures of star formation rates from Infrared (Herschel) and UV (GALEX) emissions of galaxies in the HerMES fields

The reliability of infrared (IR) and ultraviolet (UV) emissions to measure star formation rates in galaxies is investigated for a large sample of galaxies observed with the SPIRE and PACS instruments on Herschel as part of the HerMES project. We build flux-limited 250 micron samples of sources at redshift z<1, cross-matched with the Spitzer/MIPS and GALEX catalogues. About 60 % of the Herschel sources are detected in UV. The total IR luminosities, L_IR, of the sources are estimated using a SED-fitting code that fits to fluxes between 24 and 500 micron. Dust attenuation is discussed on the basis of commonly-used diagnostics: the L_IR/L_UV ratio and the slope, beta, of the UV continuum. A mean dust attenuation A_UV of ~ 3 mag is measured in the samples. L_IR/L_UV is found to correlate with L_IR. Galaxies with L_IR > 10 ^{11} L_sun and 0.5< z<1 exhibit a mean dust attenuation A_UV about 0.7 mag lower than that found for their local counterparts, although with a large dispersion. Our galaxy samples span a large range of beta and L_IR/L_UV values which, for the most part, are distributed between the ranges defined by the relations found locally for starburst and normal star-forming galaxies. As a consequence the recipe commonly applied to local starbursts is found to overestimate the dust attenuation correction in our galaxy sample by a factor ~2-3 .

astro-ph.CO↗

arXiv2009

Star formation and dust extinction properties of local galaxies from AKARI-GALEX All-Sky Surveys: First results from most secure multiband sample from FUV to FIR

The AKARI All-Sky Survey provided the first bright point source catalog detected at 90um. Starting from this catalog, we selected galaxies by matching AKARI sources with those in the IRAS PSCz. Next, we have measured total GALEX FUV and NUV flux densities. Then, we have matched this sample with SDSS and 2MASS galaxies. By this procedure, we obtained the final sample which consists of 607 galaxies. If we sort the sample with respect to 90um, their average SED shows a coherent trend: the more luminous at 90um, the redder the global SED becomes. The M_r--NUV-r color-magnitude relation of our sample does not show bimodality, and the distribution is centered on the green valley between the blue cloud and red sequence seen in optical surveys. We have established formulae to convert FIR luminosity from AKARI bands to the total infrared (IR) luminosity L_TIR. With these formulae, we calculated the star formation directly visible with FUV and hidden by dust. The luminosity related to star formation activity (L_SF) is dominated by L_TIR even if we take into account the far-infrared (FIR) emission from dust heated by old stars. At high star formation rate (SFR) (> 20 Msun yr^-1), the fraction of directly visible SFR, SFR_FUV, decreases. We also estimated the FUV attenuation A_FUV from FUV-to-total IR (TIR) luminosity ratio. We also examined the L_TIR/L_FUV-UV slope (FUV- NUV) relation. The majority of the sample has L_TIR/L_FUV ratios 5 to 10 times lower than expected from the local starburst relation, while some LIRGs and all the ULIRGs of this sample have higher L_TIR/L_FUV ratios. We found that the attenuation indicator L_TIR/L_FUV is correlated to the stellar mass of galaxies, M*, but there is no correlation with specific SFR (SSFR), SFR/M*, and dust attenuation L_TIR/L_FUV. (abridged)

astro-ph.CO↗

arXiv2009

Deep Spitzer 24mic COSMOS imaging -- I. The evolution of luminous dusty galaxies - Confronting the models

We present the first results obtained from the identification of ~30,000 sources in the 24mic observations of the COSMOS field at S24>~80muJy. Using accurate photo-z's and extrapolations of the counts at faint fluxes we resolve with unprecedented detail the build-up of the mid-IR background across cosmic ages. We find that ~50% and ~80% of the 24mic background intensity originate from galaxies at z<~1 and z<~2 respectively, supporting the scenario where highly obscured sources at very high redshifts (z>~2) contribute only marginally to the CIB. Assuming flux-limited selections at optical wavelengths, we also find that the fraction of i-band sources with 24mic detection strongly increases up to z~2 as a consequence of the rapid evolution that star-forming galaxies have undergone with lookback time. Nonetheless this rising trend shows a clear break at z~1.3, probably due to k-correction effects implied by the complexity of SEDs in the mid-IR. Finally, we compare our results with the predictions from different models of galaxy formation. We note that semi-analytical formalisms fail to reproduce the redshift distributions observed at 24mic. Furthermore the simulated galaxies exhibit R-K colors much bluer than observed and the predicted K-band fluxes are systematically underestimated at z>0.5. Unless these discrepancies result from an incorrect treatment of extinction they may reflect an underestimate of the predicted density of high-z massive sources with strong star formation, which would point to more fundamental processes that are still not fully controlled in the simulations. The most recent backward evolution scenarios reproduce reasonably well the flux/redshift distribution of 24mic sources up to z~3, although none of them is able to exactly match our results at all redshifts. [Abridged]

astro-ph.CO↗

arXiv2009

GALEX-SDSS Catalogs for Statistical Studies

We present a detailed study of the Galaxy Evolution Explorer's photometric catalogs with special focus on the statistical properties of the All-sky and Medium Imaging Surveys. We introduce the concept of primaries to resolve the issue of multiple detections and follow a geometric approach to define clean catalogs with well-understood selection functions. We cross-identify the GALEX sources (GR2+3) with Sloan Digital Sky Survey (DR6) observations, which indirectly provides an invaluable insight about the astrometric model of the UV sources and allows us to revise the band merging strategy. We derive the formal description of the GALEX footprints as well as their intersections with the SDSS coverage along with analytic calculations of their areal coverage. The crossmatch catalogs are made available for the public. We conclude by illustrating the implementation of typical selection criteria in SQL for catalog subsets geared toward statistical analyses, e.g., correlation and luminosity function studies.

astro-ph.CO↗