Undetected Galaxies Research Articles

Euclid preparation. LIII. LensMC, weak lensing cosmic shear measurement with forward modelling and Markov Chain Monte Carlo sampling

is a weak lensing shear measurement method developed for and Stage-IV surveys. It is based on forward modelling in order to deal with convolution by a point spread function (PSF) with comparable size to many galaxies, sampling the posterior distribution of galaxy parameters via Markov chain Monte Carlo, and marginalisation over nuisance parameters for each of the 1.5 billion galaxies observed by We quantified the scientific performance through high-fidelity images based on the Flagship simulations and emulation of the VIS images, realistic clustering with a mean surface number density of $ arcmin^ for galaxies, and $ arcmin^ for stars, and a diffraction-limited chromatic PSF with a full width at half maximum of $ $ and spatial variation across the field of view. measured objects with a density of $ arcmin^ in $4500 deg^2 $. The total shear bias was broken down into measurement (our main focus here) and selection effects (which will be addressed in future work). We found measurement multiplicative and additive biases of $m_1=(-3.6 $, $m_2=(-4.3 $, $c_1=(-1.78 $, and $c_2=(0.09 $; a large detection bias with a multiplicative component of $1.2 $ and an additive component of $-3 $; and a measurement PSF leakage of $ $ and $ $. When model bias is suppressed, the obtained measurement biases are close to requirement and largely dominated by undetected faint galaxies ($-5 $). Although significant, model bias will be straightforward to calibrate given its weak sensitivity on galaxy morphology parameters. is publicly available at

The HYENAS project: a prediction for the X-ray undetected galaxy groups

Abstract Galaxy groups contain the majority of bound mass with a significant portion of baryons due to the combination of halo mass and abundance (Cui 2024). Hence they serve as a crucial missing piece in the puzzle of galaxy formation and the evolution of large-scale structures in the Universe. In observations, mass-complete group catalogues are normally derived from galaxy redshift surveys detected through various three-dimensional group-finding algorithms. Confirming the reality of such groups, particularly in the X-rays, is critical for ensuring robust studies of galaxy evolution in these environments. Recent works have reported numerous optical groups that are X-ray undetected (see, e.g. Popesso et al. 2024), sparking debates regarding the reasons for the unexpectedly low hot gas fraction in galaxy groups. To address this issue, we utilise zoomed-in simulations of galaxy groups from the novel Hyenas project to explore the range of hot gas fractions within galaxy groups and investigate the intrinsic factors behind the observed variability in X-ray emission. We find that the halo formation time can play a critical role – we see that groups in halos that formed earlier exhibit up to an order of magnitude brighter X-ray luminosities compared to those formed later. This suggests that undetected X-ray groups are preferentially late-formed halos and highlights the connection between gas fraction and halo formation time in galaxy groups. Accounting for these biases in galaxy group identification is essential for advancing our understanding of galaxy formation and achieving precision in cosmological studies.

The statistics and environments of hostless supernovae

ABSTRACT Transient surveys routinely detect supernovae (SNe) without obvious host galaxies. To understand the demographics of these ‘hostless’ SNe and to constrain the possible host properties, we identify 161 SNe reported to the Transient Name Server since 2016 that do not have hosts catalogued from pre-explosion wide-field galaxy surveys. Using forced aperture photometry, we detect excess flux around only 56 of these SNe. Both thermonuclear and core-collapse (CC) SNe are present in our sample. Compared to flux-limited SNe samples with known hosts, superluminous supernovae (SLSNe), particularly hydrogen-deficient SLSNe, are over-represented here relative to all other SNe types; among CC SNe, there is also a higher fraction of interacting SNe than non-interacting. On the low-luminosity side, seven SNe have host absolute magnitude upper limits fainter than Mg = −12, about 1 per cent of the Small Magellanic Cloud’s luminosity; the faintest limits are close to the luminosity of globular clusters or ultra-faint dwarf galaxies (Mg ≃ −8). Fitting multiband forced photometry, 11 SNe have host stellar masses <106 M⊙ assuming quiescent hosts, and 13 SNe have host stellar masses <105 M⊙ assuming star-forming hosts. The spatial distribution of hostless SNe indicates that the majority are not associated with known galaxy groups and clusters, ruling out intracluster stellar light as the primary contributor of such SNe. Hostless Type Ia SNe tend to be more luminous and slow-fading than SNe Ia with known host galaxies, implying a hidden population of low-mass and star-forming hosts. We conclude that any undetected host galaxies are likely star-forming dwarfs in the field.

SIMPLE: Simple Intensity Map Producer for Line Emission

We present the Simple Intensity Map Producer for Line Emission (Simple), a public code for quickly simulating mock line-intensity maps, and an analytical framework for modeling intensity maps including observational effects. Simple can be applied to any spectral line sourced by galaxies. The Simple code is based on lognormal mock catalogs of galaxies including positions and velocities and assigns luminosities following the luminosity function. After applying a selection function to distinguish between detected and undetected galaxies, the code generates an intensity map, which can be modified with anisotropic smoothing, noise, a mask, and sky subtraction, and it calculates the power spectrum multipoles. We show that the intensity auto-power spectrum and the galaxy-intensity cross-power spectrum agree well with the analytical estimates in real space. We derive and show that the sky subtraction suppresses the intensity autopower spectrum and the cross-power spectrum on scales larger than the size of an individual observation. As an example application, we make forecasts for the sensitivity of an intensity mapping experiment similar to the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) to the cross-power spectrum of Lyα-emitting galaxies and the Lyα intensity. We predict that HETDEX will measure the galaxy-intensity cross-power spectrum with a high signal-to-noise ratio on scales of 0.04 h Mpc−1 < k < 1 h Mpc−1.

ALMA Lensing Cluster Survey: average dust, gas, and star-formation properties of cluster and field galaxies from stacking analysis

ABSTRACT We develop new tools for continuum and spectral stacking of Atacama Large Millimeter/submillimeter Array (ALMA) data, and apply these to the ALMA Lensing Cluster Survey. We derive average dust masses, gas masses, and star-formation rates (SFRs) from the stacked observed 260-GHz continuum of 3402 individually undetected star-forming galaxies, of which 1450 are cluster galaxies and 1952 field galaxies, over three redshift and stellar mass bins (over z = 0–1.6 and log$M_{*} \, [{\rm M}_{\odot }] = 8$–11.7), and derive the average molecular gas content by stacking the emission line spectra in a SFR-selected subsample. The average SFRs and specific SFRs of both cluster and field galaxies are lower than those expected for main-sequence (MS) star-forming galaxies, and only galaxies with stellar mass of log$M_{*} \, [{\rm M}_{\odot }] = 9.35$–10.6 show dust and gas fractions comparable with those in the MS. The ALMA-traced average ‘highly obscured’ SFRs are typically lower than the SFRs observed from optical to near-infrared spectral analysis. Cluster and field galaxies show similar trends in their contents of dust and gas, even when field galaxies were brighter in the stacked maps. From spectral stacking we find a potential CO (J = 4 → 3) line emission (signal-to-noise ratio being ∼4) when stacking cluster and field galaxies with the highest SFRs.

Panchromatic Photometry of Low-redshift, Massive Galaxies Selected from SDSS Stripe 82

The broadband spectral energy distribution of a galaxy encodes valuable information on its stellar mass, star formation rate (SFR), dust content, and possible fractional energy contribution from nonstellar sources. We present a comprehensive catalog of panchromatic photometry, covering 17 bands from the far-ultraviolet to 500 μm, for 2685 low-redshift (z = 0.01–0.11), massive (M * > 1010 M ⊙) galaxies selected from the Stripe 82 region of the Sloan Digital Sky Survey, one of the largest areas with relatively deep, uniform observations over a wide range of wavelengths. Taking advantage of the deep optical coadded images, we develop a hybrid approach for matched-aperture photometry of the multiband data. We derive robust uncertainties and upper limits for undetected galaxies, deblend interacting/merging galaxies and sources in crowded regions, and treat contamination by foreground stars. We perform spectral energy distribution fitting to derive the stellar mass, SFR, and dust mass, critically assessing the influence of flux upper limits for undetected photometric bands and applying corrections for systematic uncertainties based on extensive mock tests. Comparison of our measurements with those of commonly used published catalogs reveals good agreement for the stellar masses. While the SFRs of galaxies on the star-forming main sequence show reasonable consistency, galaxies in and below the green valley show considerable disagreement between different sets of measurements. Our analysis suggests that one should incorporate the most accurate and inclusive photometry into the spectral energy distribution analysis, and that care should be exercised in interpreting the SFRs of galaxies with moderate to weak star formation activity.

Sky subtraction in an era of low surface brightness astronomy

ABSTRACT The Vera C. Rubin Observatory Wide-Fast Deep sky survey will reach unprecedented surface brightness depths over tens of thousands of square degrees. Surface brightness photometry has traditionally been a challenge. Current algorithms which combine object detection with sky estimation systematically oversubtract the sky, biasing surface brightness measurements at the faint end and destroying or severely compromising low surface brightness light. While it has recently been shown that properly accounting for undetected faint galaxies and the wings of brighter objects can in principle recover a more accurate sky estimate, this has not yet been demonstrated in practice. Obtaining a consistent spatially smooth underlying sky estimate is particularly challenging in the presence of representative distributions of bright and faint objects. In this paper, we use simulations of crowded and uncrowded fields designed to mimic Hyper Suprime-Cam data to perform a series of tests on the accuracy of the recovered sky. Dependence on field density, galaxy type, and limiting flux for detection are all considered. Several photometry packages are utilized: source extractor, gnuastro, and the LSST science pipelines. Each is configured in various modes, and their performance at extreme low surface brightness analysed. We find that the combination of the source extractor software package with novel source model masking techniques consistently produce extremely faint output sky estimates, by up to an order of magnitude, as well as returning high fidelity output science catalogues.

Stellar mass fraction and quasar accretion disk size in SDSS J1004+4112 from photometric follow-up

AbstractThe gravitational lens SDSS J1004+4112 was the first discovered system where a background quasar is lensed by a galaxy cluster instead of a single galaxy. We use the 14.5-year r-band light curves together with the recently measured time delay of the fourth brightest quasar image (Munõz et al. (2022)) and the mass model from Forés-Toribio et al. (2022) to study the microlensing effect in this system. We constrain the quasar accretion disk size to light-days at 2407Å in the restframe which is compatible with most previous estimates. We also infer the fraction of mass in stars at the positions of the quasar images: $${\alpha _A} = 0.058_{ - 0.032}^{ + 0.024},{\alpha _B} = 0.048_{ - 0.014}^{ + 0.032},{\alpha _C} = 0.018_{ - 0.018}^{ + 0.015}$$ and $${\alpha _D} = 0.008_{ - 0.008}^{ + 0.033}$$ . The stellar fraction estimates are reasonable for intracluster medium although the stellar fractions at images A and B are slightly larger, suggesting the presence of a near undetected galaxy.

The Fornax Deep Survey with the VST

Context.Low surface brightness (LSB) dwarf galaxies in galaxy clusters are an interesting group of objects as their contribution to the galaxy luminosity function and their evolutionary paths are not yet clear. Increasing the completeness of our galaxy catalogs is crucial for understanding these galaxies, which have effective surface brightnesses below 23 mag arcsec−2(in optical). Progress is continuously being made via the performance of deep observations, but detection depth and the quantification of the completeness can also be improved via the application of novel approaches in object detection. For example, the Fornax Deep Survey (FDS) has revealed many faint galaxies that can be visually detected from the images down to a surface brightness level of 27 mag arcsec−2, whereas traditional detection methods, such as using Source Extractor (SE), fail to find them.Aims.In this work we use a max-tree based object detection algorithm (Max-Tree Objects, MTO) on the FDS data in order to detect previously undetected LSB galaxies. After extending the existing Fornax dwarf galaxy catalogs with this sample, our goal is to understand the evolution of LSB dwarfs in the cluster. We also study the contribution of the newly detected galaxies to the faint end of the luminosity function.Methods.We test the detection completeness and parameter extraction accuracy of MTO using simulated and real images. We then apply MTO to the FDS images to identify LSB candidates. The identified objects are fitted with 2D Sérsic models using GALFIT and classified as imaging artifacts, likely cluster members, or background galaxies based on their morphological appearance, colors, and structure.Results.With MTO, we are able to increase the completeness of our earlier FDS dwarf catalog (FDSDC) 0.5–1 mag deeper in terms of total magnitude and surface brightness. Due to the increased accuracy in measuring sizes of the detected objects, we also add many small galaxies to the catalog that were previously excluded as their outer parts had been missed in detection. We detect 265 new LSB dwarf galaxies in the Fornax cluster, which increases the total number of known dwarfs in Fornax to 821. Using the whole cluster dwarf galaxy population, we show that the luminosity function has a faint-end slope ofα= −1.38 ± 0.02. We compare the obtained luminosity function with different environments studied earlier using deep data but do not find any significant differences. On the other hand, the Fornax-like simulated clusters in the IllustrisTNG cosmological simulation have shallower slopes than found in the observational data. We also find several trends in the galaxy colors, structure, and morphology that support the idea that the number of LSB galaxies is higher in the cluster center due to tidal forces and the age dimming of the stellar populations. The same result also holds for the subgroup of large LSB galaxies, so-called ultra-diffuse galaxies.

The ALPINE-ALMA [CII] survey: The population of [CII]-undetected galaxies and their role in the L[CII]-SFR relation

The [CII] 158 μm emission line represents one of the most profitable tools for the investigation of the high-redshift galaxies in the early Universe so far. Being one of the brightest cooling lines in the rest-frame far-infrared regime of star-forming galaxies, it has been successfully exploited as a tracer of the star-formation rate (SFR) in local sources. The picture is more complex at higher redshifts, where its usability in this context is still under investigation. Recent results from the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) survey suggest that there is no (or weak) evolution of the L[CII]-SFR relation up to z ∼ 6, but their reliability is hampered by the presence of a large population of [CII] nondetected galaxies. In this work, we characterize the population of [CII] nondetections in ALPINE. By stacking their ALMA spectra, we obtained a signal detected at ∼5.1σ, resulting in a [CII] luminosity of log(L[CII]/L⊙)∼7.8. When combining this value with those from the [CII] detections, we found a L[CII]-SFR relation with a slope b = 1.14 ± 0.11, which is in agreement within the uncertainties both with the linear relation found in the local Universe and with the previous findings from ALPINE at z ∼ 5. This suggests that the [CII] line can be considered a good tracer of star formation up to the distant Universe. Finally, we show that the galaxies of our sample that deviate from the observed L[CII]-SFR relation most could suffer from a less precise redshift estimation, perhaps artificially reducing their [CII] luminosity. In this respect, we claim that there is no evidence in favor of a deficit of [CII] content in high-z galaxies, in contrast with earlier studies.

New Tests of Milli-lensing in the Blazar PKS 1413 + 135

Abstract Symmetric achromatic variability (SAV) is a rare form of radio variability in blazars that has been attributed to gravitational milli-lensing by a ∼102–105 M ⊙ mass condensate. Four SAVs have been identified between 1980 and 2020 in the long-term radio monitoring data of the blazar PKS 1413 + 135. We show that all four can be fitted with the same, unchanging, gravitational lens model. If SAV is due to gravitational milli-lensing, PKS 1413 + 135 provides a unique system for studying active galactic nuclei with unprecedented microarcsecond resolution, as well as for studying the nature of the milli-lens itself. We discuss two possible candidates for the putative milli-lens: a giant molecular cloud hosted in the intervening edge-on spiral galaxy, and an undetected dwarf galaxy with a massive black hole. We find a significant dependence of SAV crossing time on frequency, which could indicate a fast shock moving in a slower underlying flow. We also find tentative evidence for a 989 day periodicity in the SAVs, which, if real, makes possible the prediction of future SAVs: the next three windows for possible SAVs begin in 2022 August, 2025 May, and 2028 February.

Measuring the Total Ultraviolet Light from Galaxy Clusters at z = 0.5–1.6: The Balance of Obscured and Unobscured Star Formation

Abstract Combined observations from UV to IR wavelengths are necessary to fully account for the star formation in galaxy clusters. Low-mass galaxies with log ( M ∗ / M ⊙ ) &lt; 10 are typically not individually detected, particularly at higher redshifts (z ∼ 1–2) where galaxy clusters are undergoing rapid transitions from hosting mostly active, dust-obscured star-forming galaxies to hosting quiescent, passive galaxies. To account for these undetected galaxies, we measure the total light emerging from GALEX/near-UV stacks of galaxy clusters at z = 0.5–1.6. Combined with existing measurements from Spitzer, WISE, and Herschel, we study the average UV through far-IR spectral energy distribution (SED) of clusters. From the SEDs, we measure the total stellar mass and amount of dust-obscured and unobscured star formation arising from all cluster-member galaxies, including the low-mass population. The relative fraction of unobscured star formation we observe in the UV is consistent with what is observed in field galaxies. There is tentative evidence for lower than expected unobscured star formation at z ∼ 0.5, which may arise from rapid redshift evolution in the low-mass quenching efficiency in clusters reported by other studies. Finally, the GALEX data place strong constraints on derived stellar-to-halo mass ratios at z &lt; 1, which anticorrelate with the total halo mass, consistent with trends found from local X-ray observations of clusters. The data exhibit steeper slopes than implementations of the cluster star formation efficiency in semianalytical models.

Origin of Weak Mg ii and Higher-ionization Absorption Lines in Outflows from Intermediate-redshift Dwarf Galaxies

Abstract Observations at intermediate redshifts reveal the presence of numerous compact, weak Mg ii absorbers with near to supersolar metallicities, often surrounded by extended regions that produce C iv and/or O vi absorption, in the circumgalactic medium at large impact parameters from luminous galaxies. Their origin and nature remain unclear. We hypothesize that undetected satellite dwarf galaxies are responsible for producing some of these weak Mg ii absorbers. We test our hypothesis using gas dynamical simulations of galactic outflows from a dwarf galaxy with a halo mass of 5 × 109 M ⊙, as might be falling into a larger L* halo at z = 2. We find that thin, filamentary, weak Mg ii absorbers (≲100 pc) are produced in two stages: (1) when shocked core-collapse supernova (SN II)–enriched gas descending in a galactic fountain gets shock compressed by upward flows driven by subsequent SN II and cools (phase 1) and, later, (2) during an outflow driven by Type Ia supernovae that shocks and sweeps up pervasive SN II–enriched gas, which then cools (phase 2). The Mg ii absorbers in our simulations are continuously generated by shocks and cooling with moderate metallicity ∼0.1–0.2 Z ⊙ but low column density &lt;1012 cm−2. They are also surrounded by larger (0.5–1 kpc) C iv absorbers that seem to survive longer. Larger-scale (&gt;1 kpc) C iv and O vi clouds are also produced in both expanding and shocked SN II–enriched gas. Observable ion distributions from our models appear well converged at our standard resolution (12.8 pc). Our simulation highlights the possibility of dwarf galactic outflows producing highly enriched multiphase gas.

New Horizons Observations of the Cosmic Optical Background

Abstract We used existing data from the New Horizons Long-range Reconnaissance Imager (LORRI) to measure the optical-band (0.4 ≲ λ ≲ 0.9 μm) sky brightness within seven high–Galactic latitude fields. The average raw level measured while New Horizons was 42–45 au from the Sun is 33.2 ± 0.5 nW m−2 sr−1. This is ∼10× as dark as the darkest sky accessible to the Hubble Space Telescope, highlighting the utility of New Horizons for detecting the cosmic optical background (COB). Isolating the COB contribution to the raw total required subtracting scattered light from bright stars and galaxies, faint stars below the photometric detection limit within the fields, and diffuse Milky Way light scattered by infrared cirrus. We removed newly identified residual zodiacal light from the IRIS 100 μm all-sky maps to generate two different estimates for the diffuse Galactic light. Using these yielded a highly significant detection of the COB in the range 15.9 ± 4.2 (1.8 stat., 3.7 sys.) nW m−2 sr−1 to 18.7 ± 3.8 (1.8 stat., 3.3 sys.) nW m−2 sr−1 at the LORRI pivot wavelength of 0.608 μm. Subtraction of the integrated light of galaxies fainter than the photometric detection limit from the total COB level left a diffuse flux component of unknown origin in the range 8.8 ± 4.9 (1.8 stat., 4.5 sys.) nW m−2 sr−1 to 11.9 ± 4.6 (1.8 stat., 4.2 sys.) nW m−2 sr−1. Explaining it with undetected galaxies requires the assumption that the galaxy count faint-end slope steepens markedly at V &gt; 24 or that existing surveys are missing half the galaxies with V &lt; 30.

Abundance of dwarf galaxies around low-mass spiral galaxies in the Local Volume

The abundance of satellite dwarf galaxies has long been considered a crucial test for the current model of cosmology leading to the well-known missing satellite problem. Recent advances in simulations and observations have allowed the study of dwarf galaxies around host galaxies in more detail. Using the Dark Energy Camera we surveyed a 72 deg2 area of the nearby Sculptor group, also encompassing the two low-mass Local Volume galaxies NGC 24 and NGC 45 residing behind the group, to search for as yet undetected dwarf galaxies. Apart from the previously known dwarf galaxies we found only two new candidates down to a 3σ surface brightness detection limit of 27.4 r mag arcsec−2. Both systems are in projection close to NGC 24. However, one of these candidates could be an ultra-diffuse galaxy associated with a background galaxy. We compared the number of known dwarf galaxy candidates around NGC 24, NGC 45, and five other well-studied low-mass spiral galaxies (NGC 1156, NGC 2403, NGC 5023, M 33, and the LMC) with predictions from cosmological simulations, and found that for the stellar-to-halo mass models considered, the observed satellite numbers tend to be on the lower end of the expected range. This could mean either that there is an overprediction of luminous subhalos in ΛCDM or that we are missing some of the satellite members due to observational biases.

Observations of [OI]63 μm line emission in main-sequence galaxies at z ∼ 1.5

ABSTRACT We present Herschel–PACS spectroscopy of four main-sequence star-forming galaxies at z ∼ 1.5. We detect [OI]63 μm line emission in BzK-21000 at z = 1.5213, and measure a line luminosity, $L_{\rm [O\, {\small I}]63\, \mu m} = (3.9\pm 0.7)\times 10^9$ L⊙. Our PDR modelling of the interstellar medium in BzK-21000 suggests a UV radiation field strength, G ∼ 320G0, and gas density, n ∼ 1800 cm−3, consistent with previous LVG modelling of the molecular CO line excitation. The other three targets in our sample are individually undetected in these data, and we perform a spectral stacking analysis which yields a detection of their average emission and an [O i]63 μm line luminosity, $L_{\rm [O\, {\small I}]63\, \mu m} = (1.1\pm 0.2)\times 10^9$ L⊙. We find that the implied luminosity ratio, $L_{\rm [O\, {\small I}]63\, \mu m}/L_{\rm IR}$, of the undetected BzK-selected star-forming galaxies broadly agrees with that of low-redshift star-forming galaxies, while BzK-21000 has a similar ratio to that of a dusty star-forming galaxy at z ∼ 6. The high [O i]63 μm line luminosities observed in BzK-21000 and the z ∼ 1−3 dusty and sub-mm luminous star-forming galaxies may be associated with extended reservoirs of low density, cool neutral gas.

γ-ray emission in radio galaxies under the VLBI scope

Aims. This is the second paper in our series studying the evolution of parsec-scale radio emission in radio galaxies in the Southern Hemisphere. Following our study of the radio and high-energy properties of γ-ray-emitting sources, here we investigate the kinematic and spectral properties of the parsec-scale jets of radio galaxies that have not yet been detected by the Fermi Large Area Telescope (Fermi-LAT) instrument on board NASA’s Fermi Gamma-ray Space Telescope. For many sources, these results represent the first milliarcsecond resolution information in the literature. These studies were conducted within the framework of the Tracking Active Nuclei with Austral Milliarcsecond Interferometry (TANAMI) monitoring program and in the context of high-energy γ-ray observations from Fermi-LAT. Methods. We took advantage of the regular 8.4 GHz and 22.3 GHz Very Long Baseline Interferometry (VLBI) observations provided by the TANAMI monitoring program, and explored the kinematic properties of six γ-ray-faint radio galaxies. We complemented this with ∼8.5 years of Fermi-LAT data, deriving updated upper limits on the γ-ray emission from this subsample of TANAMI radio galaxies. We included publicly available VLBI kinematics of γ-ray-quiet radio galaxies monitored by the MOJAVE program and performed a consistent Fermi-LAT analysis. We combined these results with those from our previous paper to construct the largest sample of radio galaxies with combined VLBI and γ-ray measurements to date. The connection between parsec-scale jet emission and high-energy properties in the misaligned jets of radio galaxies was explored. Results. For the first time, we report evidence of superluminal motion up to βapp = 3.6 in the jet of the γ-ray-faint radio galaxy PKS 2153−69. We find a clear trend of higher apparent speed as a function of distance from the jet core, which indicates that the jet is still being accelerated on scales of tens of parsecs, or ∼105 Rs, corresponding to the end of the collimation and acceleration zone in nearby radio galaxies. We find evidence of subluminal apparent motion in the jets of PKS 1258−321 and IC 4296, and no measurable apparent motion for PKS 1549−79, PKS 1733−565, and PKS 2027−308. For all these sources, TANAMI provides the first multi-epoch kinematic analysis on parsec scales. We then compare the VLBI properties of γ-ray-detected and undetected radio galaxies, and find that the two populations show a significantly different distribution of median core flux density, and, possibly, of median core brightness temperature. In terms of correlation between VLBI and γ-ray properties, we find a significant correlation between median core flux density and γ-ray flux, but no correlation with typical Doppler boosting indicators such as median core brightness temperature and core dominance. Conclusions. Our study suggests that high-energy emission from radio galaxies is related to parsec-scale radio emission from the inner jet, but is not driven by Doppler boosting effects, in contrast to the situation in their blazar counterparts. This implies that γ-ray loudness does not necessarily reflect a higher prevalence of boosting effects.

A search for γ-ray emission from a sample of local Universe low-frequency selected radio galaxies

ABSTRACT Radio galaxies are uncommon γ-ray emitters, and only low-redshift radio galaxies are detected with the Fermi Large Area Telescope (Fermi-LAT). However, they offer potential insights into the emission mechanisms of active galaxies, particularly as the alignment of their jets with respect to the Earth means that, unlike blazars, their emission is not necessarily jet dominated. We use the Fermi-LAT data to perform an unbiased survey of 78 radio galaxies from the Bologna complete sample in order to search for new γ-ray-emitting radio galaxies. We observe statistically significant γ-ray emission from four of the six known Fermi-LAT-detected radio galaxies included in this sample, and find some evidence for γ-ray emission spatially coincident with four previously undetected radio galaxies. As a large parameter space is searched, we calculate a probability distribution to compute the look-elsewhere effect. We find that these four spatially coincident sub-threshold γ-ray excesses are most likely a chance association, and are unlikely to be emission from the radio galaxies. Upper limits on flux are calculated for the radio galaxies from which no γ-ray emission is observed.

Euclid preparation

In modern weak-lensing surveys, the common approach to correct for residual systematic biases in the shear is to calibrate shape measurement algorithms using simulations. These simulations must fully capture the complexity of the observations to avoid introducing any additional bias. In this paper we study the importance of faint galaxies below the observational detection limit of a survey. We simulate simplified Euclid VIS images including and excluding this faint population, and measure the shift in the multiplicative shear bias between the two sets of simulations. We measure the shear with three different algorithms: a moment-based approach, model fitting, and machine learning. We find that for all methods, a spatially uniform random distribution of faint galaxies introduces a shear multiplicative bias of the order of a few times 10−3. This value increases to the order of 10−2 when including the clustering of the faint galaxies, as measured in the Hubble Space Telescope Ultra-Deep Field. The magnification of the faint background galaxies due to the brighter galaxies along the line of sight is found to have a negligible impact on the multiplicative bias. We conclude that the undetected galaxies must be included in the calibration simulations with proper clustering properties down to magnitude 28 in order to reach a residual uncertainty on the multiplicative shear bias calibration of a few times 10−4, in line with the 2 × 10−3 total accuracy budget required by the scientific objectives of the Euclid survey. We propose two complementary methods for including faint galaxy clustering in the calibration simulations.

Multi-component Decomposition of Cosmic Infrared Background Fluctuations

Abstract The near-infrared background between 0.5 and 2 μm contains a wealth of information related to radiative processes in the universe. Infrared background anisotropies encode the redshift-weighted total emission over cosmic history, including any spatially diffuse and extended contributions. The anisotropy power spectrum is dominated by undetected galaxies at small angular scales and a diffuse background of Galactic emission at large angular scales. In addition to these known sources, the infrared background also arises from intrahalo light (IHL) at z &lt; 3 associated with tidally stripped stars during galaxy mergers. Moreover, it contains information on the very first galaxies from the epoch of reionization (EoR). The EoR signal has a spectral energy distribution (SED) that goes to zero near optical wavelengths due to Lyman absorption, while other signals have spectra that vary smoothly with frequency. Due to differences in SEDs and spatial clustering, these components may be separated in a multi-wavelength-fluctuation experiment. To study the extent to which EoR fluctuations can be separated in the presence of IHL, and extragalactic and Galactic foregrounds, we develop a maximum likelihood technique that incorporates a full covariance matrix among all the frequencies at different angular scales. We apply this technique to simulated deep imaging data over a 2 × 45 deg2 sky area from 0.75 to 5 μm in 9 bands and find that such a “frequency tomography” can successfully reconstruct both the amplitude and spectral shape for representative EoR, IHL, and the foreground signals.