Herschel Extragalactic Research Articles

Cross-correlation between Planck CMB lensing potential and galaxy catalogues from HELP

ABSTRACT We present the study of cross-correlation between Cosmic Microwave Background (CMB) gravitational lensing potential map released by the Planck collaboration and photometric redshift galaxy catalogues from the Herschel Extragalactic Legacy Project (HELP), divided into four sky patches: NGP, Herschel Stripe-82, and two halves of SGP field, covering in total ∼660 deg2 of the sky. We estimate the galaxy linear bias parameter, b0, from joint analysis of cross-power spectrum and galaxy autopower spectrum using Maximum Likelihood Estimation technique to obtain values ranging from 0.70 ± 0.01 for SGP Part-2 to 1.02 ± 0.02 for SGP Part-1 field. We also estimate the amplitude of cross-correlation and find the values spanning from 0.67 ± 0.18 for SGP Part-2 to 0.80 ± 0.23 for SGP Part-1 field, respectively. For NGP and SGP Part-1 fields, the amplitude is consistent with the expected value for the standard cosmological model within $\sim 1\, \sigma$, while for Herschel Stripe-82 and SGP Part-2, we find the amplitude to be smaller than expected with $\sim 1.5\, \sigma$ and $\sim 2\, \sigma$ deviation, respectively. We perform several tests on various systematic errors to study the reason for the deviation, however, value of the amplitude turns out to be robust with respect to these errors. The only significant change in the amplitude is observed when we replace the minimum-variance CMB lensing map, used in the baseline analysis, by the lensing map derived from the CMB temperature map with deprojected thermal Sunyaev–Zeldovich signal.

Preparing for LSST data

Aims.We study how the upcoming Legacy Survey of Space and Time (LSST) data from theVera C. RubinObservatory can be employed to constrain the physical properties of normal star-forming galaxies (main-sequence galaxies). Because the majority of the observed LSST objects will have no auxiliary data, we use simulated LSST data and existing real observations to test the reliability of estimates of the physical properties of galaxies, such as their star formation rate (SFR), stellar mass (Mstar), and dust luminosity (Ldust). We focus on normal star-forming galaxies because they form the majority of the galaxy population in the universe and are therefore more likely to be observed with the LSST.Methods.We performed a simulation of LSST observations and uncertainties of 50 385 real galaxies within the redshift range 0 < z < 2.5. In order to achieve this goal, we used the unique multi-wavelength data from theHerschelExtragalactic Legacy Project (HELP) survey. Our analysis focused on two fields, ELAIS N1 and COSMOS. To obtain the physical properties of the galaxies, we fit their spectral energy distributions (SEDs) using the Code Investigating GALaxy Emission. We simulated the LSST data by convolving the SEDs fitted by employing the multi-wavelength observations. We compared the main galaxy physical properties, such as SFR,Mstar, andLdustobtained from the fit of the observed multi-wavelength photometry of galaxies (from the UV to the far-IR) to those obtained from the simulated LSST optical measurements alone.Results.We present the catalogue of simulated LSST observations for 23 291 main-sequence galaxies in the ELAIS N1 field and for 9093 galaxies in the COSMOS field. It is available in the HELP virtual observatory. The stellar masses estimated based on the LSST measurements agree with the full UV to far-IR SED estimates because they mainly depend on the UV and optical emission, which is well covered by LSST in the considered redshift range. Instead, we obtain a clear overestimate of the dust-related properties (SFR,Ldust,Mstar) estimated with the LSST alone. They are highly correlated with redshift. We investigate the cause of this overestimate and conclude that it is related to an overestimate of the dust attenuation in both UV and near-IR. We find that it is necessary to employ auxiliary rest-frame mid-IR observations, simulated UV observations, or the far-UV attenuation (AFUV)-Mstarrelation to correct for the overestimate. We also deliver the correction formula log10(SFRLSST/SFRreal) = 0.26 ⋅ z2 − 0.94 ⋅ z + 0.87. It is based on the 32 384 MS galaxies detected withHerschel.

New era of LSST data: Estimating the physical properties of main-sequence galaxies

AbstractThe main goal of the Vera C. Rubin observatory is to perform the 10 year Legacy Survey of Space and Time (LSST). This future state-of-art observatory will open the new window to study billions of galaxies from Local Universe as well as the high redshift objects. In this work we employ simulated LSST observations and uncertainties, based on the 50 385 real galaxies within the redshift range 0 < z < 2.5 from the ELAIS-N1 and COSMOS fields of the Herschel Extragalactic Legacy Project (HELP) survey, to constrain the physical properties of normal star-forming galaxies, such as their star formation rate (SFR), stellar mass (Mstar), and dust luminosity (Ldust). We fit their spectral energy distributions (SEDs) using the Code Investigating GALaxy Emission (CIGALE). The stellar masses estimated based on the LSST measurements agree with the full UV to far-IR SED, while we obtain a clear overestimate of the dust-related properties (SFR, Ldust) estimated with LSST. We investigate the cause of this result and find that it is necessary to employ auxiliary rest-frame mid-IR observations, simulated UV observations, or the far-UV attenuation (AFUV)-Mstar relation to correct for the overestimate.

HELP: the Herschel Extragalactic Legacy Project

ABSTRACT We present the Herschel Extragalactic Legacy Project (HELP). This project collates, curates, homogenizes, and creates derived data products for most of the premium multiwavelength extragalactic data sets. The sky boundaries for the first data release cover 1270 deg2 defined by the Herschel SPIRE extragalactic survey fields; notably the Herschel Multi-tiered Extragalactic Survey (HerMES) and the Herschel Atlas survey (H-ATLAS). Here, we describe the motivation and principal elements in the design of the project. Guiding principles are transparent or ‘open’ methodologies with care for reproducibility and identification of provenance. A key element of the design focuses around the homogenization of calibration, meta data, and the provision of information required to define the selection of the data for statistical analysis. We apply probabilistic methods that extract information directly from the images at long wavelengths, exploiting the prior information available at shorter wavelengths and providing full posterior distributions rather than maximum-likelihood estimates and associated uncertainties as in traditional catalogues. With this project definition paper, we provide full access to the first data release of HELP; Data Release 1 (DR1), including a monolithic map of the largest SPIRE extragalactic field at 385 deg2 and 18 million measurements of PACS and SPIRE fluxes. We also provide tools to access and analyse the full HELP data base. This new data set includes far-infrared photometry, photometric redshifts, and derived physical properties estimated from modelling the spectral energy distributions over the full HELP sky. All the software and data presented is publicly available.

A hyperluminous obscured quasar at a redshift of z ≈ 4.3

ABSTRACT In this work we report the discovery of the hyperluminous galaxy HELP_J100156.75 + 022344.7 at a photometric redshift of $z$ ≈ 4.3. The galaxy was discovered in the Cosmological Evolution Survey (COSMOS) field, one of the fields studied by the Herschel Extragalactic Legacy Project (HELP). We present the spectral energy distribution (SED) of the galaxy and fit it with the CYprus models for Galaxies and their NUclear Spectra (CYGNUS) multi-component radiative transfer models. We find that its emission is dominated by an obscured quasar with a predicted total 1–1000 μm luminosity of $3.91^{+1.69}_{-0.55} \times 10^{13}\, \mathrm{ L}_\odot$ and an active galactic nucleus (AGN) fraction of $\sim 89{{\ \rm per\ cent}}$. We also fit HELP_J100156.75 + 022344.7 with the cigale(code investigating galaxy emission) code and find a similar result. This is only the second $z$ > 4 hyperluminous obscured quasar discovered to date. The discovery of HELP_J100156.75 + 022344.7 in the ∼2 deg2 COSMOS field implies that a large number of obscured hyperluminous quasars may lie in the HELP fields, which cover ∼1300 deg2. If this is confirmed, tension between supermassive black hole evolution models and observations will be alleviated. We estimate the space density of objects like HELP_J100156.75 + 022344.7 at $z$ ≈ 4.5 to be ∼1.8 × 10−8 Mpc−3. This is slightly higher than the space density of coeval hyperluminous optically selected quasars, suggesting that the obscuring torus in $z$ > 4 quasars may have a covering factor $\gtrsim 50{{\ \rm per\ cent}}$.

HELP project - a dreamed-of multiwavelength dataset for SED fitting: The influence of used models for the main physical properties of galaxies

AbstractThe Herschel Extragalactic Legacy Project (HELP) focuses to publish an astronomical multiwavelength catalogue of millions of objects over 1300 deg2of the Herschel Space Observatory survey fields. Millions of galaxies with ultraviolet–far infrared photometry make HELP a perfect sample for testing spectral energy distribution fitting models, and to prepare tools for next-generation data. In the frame of HELP collaboration we estimated the main physical properties of all galaxies from the HELP database and we checked a new procedure to select peculiar galaxies from large galaxy sample and we investigated the influence of used modules for stellar mass estimation.

HELP: a catalogue of 170 million objects, selected at 0.36–4.5 μm, from 1270 deg2 of prime extragalactic fields

ABSTRACT We present an optical to near-infrared (NIR) selected astronomical catalogue covering 1270 deg2. This is the first attempt to systematically combine data from 23 of the premier extragalactic survey fields – the product of a vast investment of telescope time. The fields are those imaged by the Herschel Space Observatory that form the Herschel Extragalactic Legacy Project (HELP). Our catalogue of 170 million objects is constructed by a positional cross-match of 51 public surveys. This high-resolution optical, NIR, and mid-infrared catalogue is designed for photometric redshift estimation, extraction of fluxes in lower resolution far-infrared maps, and spectral energy distribution modelling. It collates, standardizes, and provides value added derived quantities including corrected aperture magnitudes and astrometry correction over the Herschel extragalactic wide fields for the first time. $grizy$ fluxes are available on all fields with g-band data reaching $5\sigma$ point-source depths in a 2 arcsec aperture of 23.5, 24.4, and 24.6 (AB) mag at the 25th, 50th, and 75th percentiles, by area covered, across all HELP fields. It has K or $K_s$ coverage over 1146 deg2 with depth percentiles of 20.2, 20.4, and 21.0 mag, respectively. The IRAC Ch 1 band is available over 273 deg2 with depth percentiles of 17.7, 21.4, and 22.2 mag, respectively. This paper defines the ‘masterlist’ objects for the first data release (DR1) of HELP. This large sample of standardized total and corrected aperture fluxes, uniform quality flags, and completeness measures provides large well-understood statistical samples over the full Herschel extragalactic sky.

Cosmic happenstance: 24-µm selected, multicomponent Herschel sources are line-of-sight projections

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 (HELP), we identify a sample of galaxies in the COSMOS field which are found to be both FIR-bright (typically $\sim 15$ mJy) and blended within the Herschel 250 $\mu$m 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 which are likely to be found at consistent ($\Delta z$ $< 0.01$) redshifts. We find that only 3 (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-$\mu$m selected, FIR-bright objects in the COSMOS field, the overwhelming majority of multi-component FIR systems are line of sight projections within the 18.1 arcsec Herschel beam, rather than physical associations.

HELP: xid+, the probabilistic de-blender forHerschelSPIRE maps

We have developed a new prior-based source extraction tool, XID+, to carry out photometry in the Herschel SPIRE maps at the positions of known sources. XID+ is developed using a probabilistic Bayesian framework which provides a natural framework in which to include prior information, and uses the Bayesian inference tool, Stan, to obtain the full posterior probability distribution on flux estimates. In this paper, we discuss the details of XID+ and demonstrate the basic capabilities and performance by running it on simulated SPIRE maps resembling the COSMOS field, and comparing to the current prior-based source extraction tool DESPHOT. We show that not only does XID+ perform better on metrics such as flux accuracy and flux uncertainty accuracy, we illustrate how obtaining the posterior probability distribution can help overcome some of the issues inherent with maximum likelihood based source extraction routines. We run XID+ on the COSMOS SPIRE maps from HerMES, using a 24 $\mathrm{\mu m}$ catalogue as a prior and show the marginalised SPIRE colour-colour plot and marginalised contribution to the cosmic infrared background at the SPIRE wavelengths. XID+ is a core tool arising from the Herschel Extragalactic Legacy Project (HELP) and we discuss how additional work within HELP providing prior information on fluxes can and will be utilised. The software is available at https://github.com/H-E-L-P/XID_plus. We also provide the data product for COSMOS. We believe this is the first time that the full posterior probability of galaxy photometry has been provided as a data product.

HELP: star formation as a function of galaxy environment withHerschel

The Herschel Extragalactic Legacy Project (HELP) brings together a vast range of data from many astronomical observatories. Its main focus is on the Herschel data, which maps dust obscured star formation over 1300 deg$^2$. With this unprecedented combination of data sets, it is possible to investigate how the star formation vs stellar mass relation (main-sequence) of star-forming galaxies depends on environment. In this pilot study we explore this question between 0.1 < z < 3.2 using data in the COSMOS field. We estimate the local environment from a smoothed galaxy density field using the full photometric redshift probability distribution. We estimate star formation rates by stacking the SPIRE data from the Herschel Multi-tiered Extragalactic Survey (HerMES). Our analysis rules out the hypothesis that the main-sequence for star-forming systems is independent of environment at 1.5 < z < 2, while a simple model in which the mean specific star formation rate declines with increasing environmental density gives a better description. However, we cannot exclude a simple hypothesis in which the main-sequence for star-forming systems is independent of environment at z < 1.5 and z > 2. We also estimate the evolution of the star formation rate density in the COSMOS field and our results are consistent with previous measurements at z < 1.5 and z > 2 but we find a $1.4^{+0.3}_{-0.2}$ times higher peak value of the star formation rate density at $z \sim 1.9$.

The HerMES Local Luminosity Function

AbstractWe exploit the Herschel Extragalactic Multi-Tiered Survey (HerMES) dataset along with ancillary multi-wavelength photometry and spectroscopy from the Spitzer Data Fusion to provide the most accurate determination to date of the local (0.02&lt;z&lt;0.5) Far-Infrared Luminosity and Star Formation Rate Function. We present and compare our results with model predictions as well as other multi-wavelength estimates of the local star formation rate density.

The warm ISM in the Sgr A region: mid-J CO, atomic carbon, ionized atomic carbon, and ionized nitrogen line observations with the Herschel/HIFI and NANTEN2/SMART Telescopes

AbstractWe present Herschel/HIFI sub-mm atomic carbon ([Ci] 3P1 – 3P0 and [Ci] 3P2 – 3P1), ionized carbon ([Cii] 2P3/2 – 2P1/2), and ionized nitrogen ([Nii] 3P1 – 3P0) line observations obtained in the frame of the Herschel Guaranteed Time HEXGAL (Herschel EXtraGALactic) key program (P. I. Rolf Güsten, MPIfR), and NANTEN2/SMART carbon monoxide (CO(J = 4 – 3)) observations of the warm gas around the Sgr A region. The spectrally resolved emission from all lines, and the corresponding line intensity ratios, show a very complex morphology. The determination of spatial and spectral (anti)correlation with known sources in the Sgr A region such as the Arched Filaments, NTF filaments, the Sickle, Quintuplet cluster, CND clouds, is ongoing work.