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Cosmic happenstance: 24-μm selected, multicomponent Herschel sources are line-of-sight projections
摘要： In this paper, we investigate the physical associations between blended far-infrared (FIR)-emitting galaxies, in order to identify the level of line-of-sight projection contamination in the single-dish Herschel data. Building on previous work, and as part of the Herschel Extragalactic Legacy Project, we identify a sample of galaxies in the COSMOS field, which are found to be both FIR-bright (typically ～15 mJy) and blended within the Herschel 250-μm beam. We identify a spectroscopic or photometric redshift for each FIR-bright source. We conduct a joint probability distribution analysis on the redshift probability density functions to determine the fraction of the FIR sources with multiple FIR-bright counterparts that are likely to be found at consistent (Δz < 0.01) redshifts. We find that only three (0.4 per cent) of the pair permutations between counterparts are >50 per cent likely to be at consistent redshifts. A majority of counterparts (72 per cent) have no overlap in their redshift probability distributions whatsoever. This is in good agreement with the results of recent simulations, which indicate that single-dish observations of the FIR sky should be strongly contaminated by line-of-sight projection effects. We conclude that for our sample of 3.6- and 24-μm selected, FIR-bright objects in the COSMOS field, the overwhelming majority of multicomponent FIR systems are line-of-sight projections within the 18.1-arcsec Herschel beam, rather than physical associations.
关键词： galaxies: statistics,galaxies: starburst,galaxies: star formation,galaxies: high redshift
更新于2025-09-23 15:22:29
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The optical morphologies of galaxies in the IllustrisTNG simulation: a comparison to Pan-STARRS observations
摘要： We have generated synthetic images of ～27 000 galaxies from the IllustrisTNG and the original Illustris hydrodynamic cosmological simulations, designed to match Pan-STARRS observations of log10(M?/M(cid:4)) ≈ 9.8–11.3 galaxies at z ≈ 0.05. Most of our synthetic images were created with the SKIRT radiative transfer code, including the effects of dust attenuation and scattering, and performing the radiative transfer directly on the Voronoi mesh used by the simulations themselves. We have analysed both our synthetic and real Pan-STARRS images with the newly developed statmorph code, which calculates non-parametric morphological diagnostics – including the Gini–M20 and concentration–asymmetry–smoothness statistics – and performs 2D S′ersic ?ts. Overall, we ?nd that the optical morphologies of IllustrisTNG galaxies are in good agreement with observations, and represent a substantial improvement compared to the original Illustris simulation. In particular, the locus of the Gini–M20 diagram is consistent with that inferred from observations, while the median trends with stellar mass of all the morphological, size and shape parameters considered in this work lie within the ～1σ scatter of the observational trends. However, the IllustrisTNG model has some dif?culty with more stringent tests, such as producing a strong morphology–colour relation. This results in a somewhat higher fraction of red discs and blue spheroids compared to observations. Similarly, the morphology–size relation is problematic: while observations show that discs tend to be larger than spheroids at a ?xed stellar mass, such a trend is not present in IllustrisTNG.
关键词： galaxies: statistics,galaxies: formation,galaxies: structure,methods: numerical,techniques: image processing
更新于2025-09-23 15:22:29
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Cross-correlation of cosmic far-infrared background anisotropies with large scale structures
摘要： We measure the cross-power spectra between luminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS)-III data release 8 (DR8) and cosmic infrared background (CIB) anisotropies from Planck and data from the Improved Reprocessing (IRIS) of the Infrared Astronomical Satellite (IRAS) at 353, 545, 857, and 3000 GHz, corresponding to 850, 550, 350 and 100 μm, respectively, in the multipole range 100 < l < 1000. Using approximately 6.5 × 10^5 photometrically determined LRGs in 7760 deg^2 of the northern hemisphere in the redshift range 0.45 < z < 0.65, we model the far-infrared background (FIRB) anisotropies with an extended version of the halo model. With these methods, we confirm the basic picture obtained from recent analyses of FIRB anisotropies with Herschel and Planck that the most efficient halo mass at hosting star forming galaxies is log(Meff/M☉) = 12.84 ± 0.15. We estimate the percentage of FIRB anisotropies correlated with LRGs as approximately 11.8%, 3.9%, 1.8%, and 1.0% of the total at 3000, 857, 545, and 353 GHz, respectively. At redshift z ～ 0.55, the bias of FIRB galaxies with respect to the dark matter density field has the value bFIRB ～ 1.45, and the mean dust temperature of FIRB galaxies is Td = 26 K. Finally, we discuss the impact of present and upcoming cross-correlations with far-infrared background anisotropies on the determination of the global star formation history and the link between galaxies and dark matter.
关键词： galaxies: statistics,large-scale structure of Universe,galaxies: evolution,cosmic background radiation,infrared: diffuse background
更新于2025-09-23 15:22:29
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Recovering the systemic redshift of galaxies from their Lyman alpha line profile
摘要： The Lyman alpha (Ly α) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km s?1 compared to the systemic redshift. This large offset hampers follow-up surveys, galaxy pair statistics, and correlations with quasar absorption lines when only Ly α is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the Ly α line pro?le. We use spectroscopic observations of Ly α emitters for which a precise measurement of the systemic redshift is available. Our sample contains 13 sources detected between z ≈ 3 and z ≈ 6 as part of various multi-unit spectroscopic explorer guaranteed time observations. We also include a compilation of spectroscopic Ly α data from the literature spanning a wide redshift range (z ≈ 0–8). First, restricting our analysis to double-peaked Ly α spectra, we ?nd a tight correlation between the velocity offset of the red peak with respect to the systemic redshift, V red peak, and the separation of the peaks. Secondly, we ?nd a correlation between V red peak and the full width at half-maximum of the Ly α line. Fitting formulas to estimate systemic redshifts of galaxies with an accuracy of ≤100 km s?1, when only the Ly α emission line is available, are given for the two methods.
关键词： ultraviolet: galaxies,galaxies: starburst,galaxies: statistics,galaxies: high-redshift
更新于2025-09-23 15:21:01
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Tidal Features at 0.05 < <i>z</i> < 0.45 in the Hyper Suprime-Cam Subaru Strategic Program: Properties and Formation Channels
摘要： We present 1201 galaxies at 0.05 < z < 0.45 that host tidal features in the first ～200 deg2 of imaging from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We select these galaxies from a sample of 21,208 galaxies with spectroscopic redshifts drawn from the Sloan Digital Sky Survey (SDSS) spectroscopic campaigns. Of these galaxies, we identify 214 shell systems and 987 stream systems. For 575 of these systems, we are additionally able to measure the (g?i) colors of the tidal features. We find evidence for star formation in a subset of the streams, with the exception of streams around massive ellipticals, and find that stream host galaxies span the full range of stellar masses in our sample. Galaxies that host shells are predominantly red and massive: we find that observable shells form more frequently around ellipticals than around disk galaxies of the same stellar mass. Although the majority of the shells in our sample are consistent with being formed by minor mergers, 15% ± 4.4% of shell host galaxies have (g?i) colors as red as their host galaxy, consistent with being formed by major mergers. These “red shell” galaxies are preferentially aligned with the major axis of the host galaxy, as previously predicted from simulations. We suggest that although the bulk of the observable shell population originates from fairly minor mergers, which preferentially form shells that are not aligned with the major axis of the galaxy, major mergers produce a significant number of observable shells.
关键词： techniques: image processing,galaxies: interactions,catalogs,galaxies: structure,galaxies: statistics
更新于2025-09-23 15:21:01
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A new method to assign galaxy cluster membership using photometric redshifts
摘要： We introduce a new effective strategy to assign group and cluster membership probabilities Pmem to galaxies using photometric redshift information. Large dynamical ranges both in halo mass and cosmic time are considered. The method takes into account the magnitude distribution of both cluster and field galaxies as well as the radial distribution of galaxies in clusters using a non-parametric formalism, and relies on Bayesian inference to take photometric redshift uncertainties into account. We successfully test the method against 1208 galaxy clusters within redshifts z = 0.05?2.58 and masses 1013.29?14.80 M(cid:12) drawn from wide field simulated galaxy mock catalogs mainly developed for the forthcoming Euclid mission. Median purity and completeness values of (55+17 ?10)% and (95+5 ?15)% are reached for galaxies brighter than 0.25 L? within r200 of each simulated halo and for a statistical photometric redshift accuracy σ((zs ? zp)/(1 + zs)) = 0.03. The mean values p = 56% and c = 93% are consistent with the median and have negligible sub-percent uncertainties. Accurate photometric redshifts (σ((zs ? zp)/(1 + zs)) (cid:46) 0.05) and robust estimates for the cluster redshift and cluster center coordinates are required. The dependence of the assignments on photometric redshift accuracy, galaxy magnitude and distance from the halo center, and halo properties such as mass, richness, and redshift are investigated. Variations in the mean values of both purity and completeness are globally limited to a few percent. The largest departures from the mean values are found for galaxies associated with distant z (cid:38) 1.5 halos, faint (～0.25 L?) galaxies, and those at the outskirts of the halo (at cluster-centric projected distances ～r200) for which the purity is decreased, ?p (cid:39) 20% at most, with respect to the mean value. The proposed method is applied to derive accurate richness estimates. A statistical comparison between the true (Ntrue) vs. estimated richness (λ = (cid:80) Pmem) yields on average to unbiased results, Log(λ/Ntrue) = ?0.0051 ± 0.15. The scatter around the mean of the logarithmic difference between λ and the halo mass is 0.10 dex for massive halos (cid:38)1014.5 M(cid:12). Our estimates could therefore be useful to constrain the cluster mass function and to calibrate independent cluster mass estimates such as those obtained from weak lensing, Sunyaev-Zel’dovich, and X-ray studies. Our method can be applied to any list of galaxy clusters or groups in both present and forthcoming surveys such as SDSS, CFHTLS, Pan-STARRS, DES, LSST, and Euclid.
关键词： galaxies: clusters: general,galaxies: groups: general,galaxies: statistics
更新于2025-09-09 09:28:46
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Towards a census of high-redshift dusty galaxies with Herschel
摘要： Context. Over the last decade a large number of dusty star-forming galaxies has been discovered up to redshift z = 2 ? 3 and recent studies have attempted to push the highly confused Herschel SPIRE surveys beyond that distance. To search for z ≥ 4 galaxies they often consider the sources with ?uxes rising from 250 μm to 500 μm (so-called “500 μm-risers”). Herschel surveys offer a unique opportunity to ef?ciently select a large number of these rare objects, and thus gain insight into the prodigious star-forming activity that takes place in the very distant Universe. Aims. We aim to implement a novel method to obtain a statistical sample of 500 μm-risers and fully evaluate our selection inspecting different models of galaxy evolution. Methods. We consider one of the largest and deepest Herschel surveys, the Herschel Virgo Cluster Survey. We develop a novel selection algorithm which links the source extraction and spectral energy distribution ?tting. To fully quantify selection biases we make end-to-end simulations including clustering and lensing. Results. We select 133 500 μm-risers over 55 deg2, imposing the criteria: S 500 > S 350 > S 250, S 250 > 13.2 mJy and S 500 > 30 mJy. Differential number counts are in fairly good agreement with models, displaying a better match than other existing samples. The estimated fraction of strongly lensed sources is 24+6 Conclusions. We present the faintest sample of 500 μm-risers down to S 250 = 13.2 mJy. We show that noise and strong lensing have an important impact on measured counts and redshift distribution of selected sources. We estimate the ?ux-corrected star formation rate density at 4 < z < 5 with the 500 μm-risers and ?nd it to be close to the total value measured in far-infrared. This indicates that colour selection is not a limiting effect to search for the most massive, dusty z > 4 sources.
关键词： galaxies: photometry,galaxies: evolution,galaxies: statistics,galaxies: high-redshift,infrared: galaxies,galaxies: star formation
更新于2025-09-04 15:30:14
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Extracting H <i>α</i> flux from photometric data in the J-PLUS survey
摘要： Aims. We present the main steps that will be taken to extract Hα emission ?ux from Javalambre Photometric Local Universe Survey (J-PLUS) photometric data. Methods. For galaxies with z (cid:46) 0.015, the Hα+[N ??] emission is covered by the J-PLUS narrow-band ?lter F660. We explore three di?erent methods to extract the Hα + [N ??] ?ux from J-PLUS photometric data: a combination of a broad-band and a narrow-band ?lter (r(cid:48) and F660), two broad-band and a narrow-band ?lter (r(cid:48), i(cid:48) and F660), and an SED-?tting based method using eight photometric points. To test these methodologies, we simulated J-PLUS data from a sample of 7511 SDSS spectra with measured Hα ?ux. Based on the same sample, we derive two empirical relations to correct the derived Hα+[N ??] ?ux from dust extinction and [N ??] contamination. Results. We ?nd that the only unbiased method is the SED-?tting based method. The combination of two ?lters underestimates the measurements of the Hα + [N ??] ?ux by 22%, while the three ?lters method are underestimated by 9%. We study the error budget of the SED-?tting based method and ?nd that, in addition to the photometric error, our measurements have a systematic uncertainty of 4.3%. Several sources contribute to this uncertainty: the di?erences between our measurement procedure and that used to derive the spectroscopic values, the use of simple stellar populations as templates, and the intrinsic errors of the spectra, which were not taken into account. Apart from that, the empirical corrections for dust extinction and [N ??] contamination add an extra uncertainty of 14%. Conclusions. Given the J-PLUS photometric system, the best methodology to extract Hα + [N ??] ?ux is the SED-?tting based method. Using this method, we are able to recover reliable Hα ?uxes for thousands of nearby galaxies in a robust and homogeneous way. Moreover, each stage of the process (emission line ?ux, dust extinction correction, and [N ??] decontamination) can be decoupled and improved in the future. This method ensures reliable Hα measurements for many studies of galaxy evolution, from the local star formation rate density, to 2D studies in spatially well-resolved galaxies or the study of environmental e?ects, up to mr(cid:48) = 21.8 (AB; 3σ detection of Hα+[N ??] emission).
关键词： methods: data analysis,galaxies: star formation,galaxies: statistics,techniques: photometric
更新于2025-09-04 15:30:14
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A Catalog of Photometric Redshift and the Distribution of Broad Galaxy Morphologies
摘要： We created a catalog of photometric redshift of ～3,000,000 SDSS galaxies annotated by their broad morphology. The photometric redshift was optimized by testing and comparing several pattern recognition algorithms and variable selection strategies, and was trained and tested on a subset of the galaxies in the catalog that had spectra. The galaxies in the catalog have i magnitude brighter than 18 and Petrosian radius greater than 5.5(cid:48)(cid:48). The majority of these objects are not included in previous SDSS photometric redshift catalogs such as the photoz table of SDSS DR12. Analysis of the catalog shows that the number of galaxies in the catalog that are visually spiral increases until redshift of ～0.085, where it peaks and starts to decrease. It also shows that the number of spiral galaxies compared to elliptical galaxies drops as the redshift increases.
关键词： galaxies: statistics,methods: data analysis,catalogs,galaxies: spiral
更新于2025-09-04 15:30:14