We investigate the relation between neutral atomic hydrogen (Hi) and dark matter halo mass (HIHM) using observations from the Deep Investigation of Neutral Gas Origins (DINGO) pilot survey 100 h data, combined with spectroscopic data from the Galaxy and Mass Assembly (GAMA) survey and photometric data from the Wide Area VISTA Extragalactic Survey (WAVES) photometric catalogue. We employ a combination of direct detections and spectral stacking to probe the Hi content of haloes across a wide mass range ( 10(10 . 5) less than or similar to M-h/M-(R) less than or similar to 10(14 . 5 )). By incorporating WAVES photometric members on top of the existing GAMA group catalogue, we present a novel approach of extending stacking analyses beyond spectroscopic completeness limits, enabling recovery of satellite Hi content otherwise missed. We find that the HIHM relation exhibits a double power-law form, with a turnover near Mh similar to 1011.2 M (R). Central galaxies dominate the halo Hi budget below M-h similar to 6 x 10(12 )M ((R)), while satellites dominate at higher halo masses. Including photometric members increases the measured Hi content in haloes above 10(13) M ((R)) by a factor of 1.5-3, highlighting the importance of gas-rich satellites in the group and cluster regime. Comparison with previous group-stacking studies shows that low-surface brightness galaxies and intra-group Hi structures contribute only a minor fraction to the total H i mass in group and cluster haloes, as the summed galaxy Hi masses are consistent with the total halo H i content.

We investigate the relation between neutral atomic hydrogen (HI) and dark matter halo mass (HIHM) using observations from the Deep Investigation of Neutral Gas Origins (DINGO) pilot survey 100h data, combined with spectroscopic data from the Galaxy and Mass Assembly (GAMA) survey and photometric data from the Wide Area VISTA Extragalactic Survey (WAVES) photometric catalog. We employ a combination of direct detections and spectral stacking to probe the HI content of halos across a wide mass range (10^10.5≲ M_h/M_⊙≲ 10^14.5). By incorporating WAVES photometric members on top of the existing GAMA group catalog, we present a novel approach of extending stacking analyses beyond spectroscopic completeness limits, enabling recovery of satellite HI content otherwise missed. We find that the HIHM relation exhibits a double power-law form, with a turnover near M_h∼ 10^11.2 M_⊙. Central galaxies dominate the halo HI budget below M_h∼ 6 × 10^12 M_⊙, while satellites dominate at higher halo masses. Including photometric members increases the measured HI content in halos above 10^13 M_⊙ by a factor of 1.5-3, highlighting the importance of gas-rich satellites in the group and cluster regime. Comparison with previous group-stacking studies shows that low-surface brightness galaxies, and intra-group HI structures contribute only a minor fraction to the total HI mass in group and cluster halos, as the summed galaxy HI masses are consistent with the total halo HI content.

The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

Galaxy Zoo is an online project to classify morphological features in extra-galactic imaging surveys with public voting. In this paper, we compare the classifications made for two different surveys, the Dark Energy Spectroscopic Instrument (DESI) imaging survey and a part of the Kilo-Degree Survey (KiDS), in the equatorial fields of the Galaxy And Mass Assembly (GAMA) survey. Our aim is to cross-validate and compare the classifications based on different imaging quality and depth. We find that generally the voting agrees globally but with substantial scatter i.e. substantial differences for individual galaxies. There is a notable higher voting fraction in favor of ``smooth'' galaxies in the DESI+\rev{{\sc zoobot}} classifications, most likely due to the difference between imaging depth. DESI imaging is shallower and slightly lower resolution than KiDS and the Galaxy Zoo images do not reveal details such as disk features \rev{and thus are missed in the {\sc zoobot} training sample}. \rev{We check against expert visual classifications and find good agreement with KiDS-based Galaxy Zoo voting.} We reproduce the results from Porter-Temple+ (2022), on the dependence of stellar mass, star-formation, and specific star-formation on the number of spiral arms. This shows that once corrected for redshift, the DESI Galaxy Zoo and KiDS Galaxy Zoo classifications agree well on population properties. The zoobot cross-validation increases confidence in its ability to compliment Galaxy Zoo classifications and its ability for transfer learning across surveys.

During its 6-year nominal mission, Euclid shall survey one third of the sky, enabling us to examine the spatial distributions of dark and luminous matter during the past 10 Gyr of cosmic history. The Euclid satellite was successfully launched on a SpaceX Falcon 9 launcher from Cape Canaveral on 1 July 2023 and is fully operational in a halo orbit around the Second Sun-Earth Lagrange point. We present an overview of the expected and unexpected findings during the early phases of the mission, in the context of technological heritage and lessons learnt. The first months of the mission were dedicated to the commissioning of the spacecraft, telescope and instruments, followed by a phase to verify the scientific performance and to carry out the in-orbit calibrations. We report that the key enabling scientific elements, the 1.2-meter telescope and the two scientific instruments, a visual imager (VIS) and a near-infrared spectrometer and photometer (NISP), show an in-orbit performance in line with the expectations from ground tests. The scientific analysis of the observations from the Early Release Observations (ERO) program done before the start of the nominal mission showed sensitivities better than the prelaunch requirements. The nominal mission started in December 2023, and we allocated a 6-month early survey operations phase to closely monitor the performance of the sky survey. We conclude with an outlook of the activities for the remaining mission in the light of the in-orbit performance.

Star-galaxy separation is a crucial step in creating target catalogues for extragalactic spectroscopic surveys. A classifier biased towards inclusivity risks including high numbers of stars, wasting fibre hours, while a more conservative classifier might overlook galaxies, compromising completeness and hence survey objectives. To avoid bias introduced by a training set in supervised methods, we employ an unsupervised machine learning approach. Using photometry from the Wide Area VISTA Extragalactic Survey (WAVES)-Wide catalogue comprising nine-band u-K-s data, we create a feature space with colours, fluxes, and apparent size information extracted by ProFound. We apply the non-linear dimensionality reduction method UMAP (Uniform Manifold Approximation and Projection) combined with the classifier hdbscan (Hierarchical Density-Based Spatial Clustering of Applications with Noise) to classify stars and galaxies. Our method is verified against a baseline colour and morphological method using a truth catalogue from Gaia, SDSS (Sloan Digital Sky Survey), GAMA (Galaxy And Mass Assembly), and DESI (Dark Energy Spectroscopic Instrument). We correctly identify 99.75 per cent of galaxies within the AB magnitude limit of Z=21.2, with an F1 score of 0.9971 +/- 0.0018 across the entire ground truth sample, compared to 0.9879 +/- 0.0088 from the baseline method. Our method's higher purity (0.9967 +/- 0.0021) compared to the baseline (0.9795 +/- 0.0172) increases efficiency, identifying 11 per cent fewer galaxy or ambiguous sources, saving approximately 70 000 fibre hours on the 4MOST (4-m Multi-Object Spectroscopic Telescope) instrument. We achieve reliable classification statistics for challenging sources including quasars, compact galaxies, and low surface brightness galaxies, retrieving 92.7 per cent, 84.6 per cent, and 99.5 per cent of them, respectively. Angular clustering analysis validates our classifications, showing consistency with expected galaxy clustering, regardless of the baseline classification.

Galaxy populations are known to exhibit a strong colour bimodality, corresponding to blue star-forming and red quiescent subpopulations. The relative abundance of the two populations has been found to vary with stellar mass and environment. In this paper, we explore the effect of environment considering different types of measurements. We choose a sample of 49, 911 galaxies with 0.05 < z < 0.18 from the Galaxy And Mass Assembly survey. We study the dependence of the fraction of red galaxies on different measures of the local environment as well as the large-scale "geometric" environment defined by density gradients in the surround- ing cosmic web. We find that the red galaxy fraction varies with the environment at fixed stellar mass. The red fraction depends more strongly on local environmental measures than on large-scale geometric environment measures. By comparing the different environmental densities, we show that no density measurement fully explains the observed environmental red fraction variation, suggesting the different measures of environmental density contain different information. We test whether the local environmental measures, when combined together, can explain all the observed environmental red fraction variation. The geometric environment has a small residual effect, and this effect is larger for voids than any other type of geometric environment. This could provide a test of the physics applied to cosmological-scale galaxy evolution simulations as it combines large-scale effects with local environmental impact.

We present early science results from Deep Investigation of Neutral Gas Origins (DINGO), an H I survey using the Australian Square Kilometre Array Pathfinder (ASKAP). Using ASKAP subarrays available during its commissioning phase, DINGO early science data were taken over similar to 60 deg(2) of the Galaxy And Mass Assembly (GAMA) 23 h region with 35.5 h integration time. We make direct detections of six known and one new sources at z < 0.01. Using H I spectral stacking, we investigate the H I gas content of galaxies at 0.04 < z < 0.09 for different galaxy colours. The results show that galaxy morphology based on optical colour is strongly linked to H I gas properties. To examine environmental impacts on the H I gas content of galaxies, three subsamples are made based on the GAMA group catalogue. The average H I mass of group central galaxies is larger than those of satellite and isolated galaxies, but with a lower H I gas fraction. We derive a variety of H I scaling relations for physical properties of our sample, including stellar mass, stellar mass surface density, NUV - r colour, specific star formation rate, and halo mass. We find that the derived H I scaling relations are comparable to other published results, with consistent trends also observed to similar to 0.5 dex lower limits in stellar mass and stellar surface density. The cosmic H I densities derived from our data are consistent with other published values at similar redshifts. DINGO early science highlights the power of H I spectral stacking techniques with ASKAP.

We construct the halo mass function (HMF) from the GAMA galaxy group catalogue over the mass range 10^12.7M_sol to 10^15.5M_sol, and find good agreement with the expectation from LambdaCDM. In comparison to previous studies, this result extends the mass range over which the HMF has now been measured over by an order of magnitude. We combine the GAMA DR4 HMF with similar data from the SDSS DR12 and REFLEX II surveys, and fit a four-parameter Murray-Robotham-Power (MRP) function, valid at z 0.1, yielding: a density normalisation of: log10 (phi Mpc^3)=-3.96[+0.55,-0.82], a high mass turn-over of: log10(M/M_sol)=14.13[+0.43,-0.40], a low mass power law slope of: alpha=-1.68[+0.21,-0.24] , and a high mass softening parameter of: beta= 0.63[+0.25,-0.11]. If we fold in the constraint on Omega_M from Planck 2018 Cosmology, we are able to reduce these uncertainties further, but this relies on the assumption that the power-law trend can be extrapolated from 10^12.7M_sol to zero mass. Throughout, we highlight the effort needed to improve on our HMF measurement: improved halo mass estimates that do not rely on calibration to simulations; reduced halo mass uncertainties needed to mitigate the strong Eddington Bias that arises from the steepness of the HMF low mass slope; and deeper wider area spectroscopic surveys. To our halo mass limit of 10^12.7 M_sol, we are directly resolving (`seeing') 41+/-5 per cent of the total mass density, i.e. Omega_[M>12.7]=0.128+/-0.016, opening the door for the direct construction of 3D dark matter mass maps at Mpc resolution.

In Galaxy And Mass Assembly Data Release 4 (GAMA DR4), we make available our full spectroscopic redshift sample. This includes 248682 galaxy spectra, and, in combination with earlier surveys, results in 330542 redshifts across five sky regions covering ~250deg^2. The redshift density, is the highest available over such a sustained area, has exceptionally high completeness (95 per cent to r_KIDS=19.65mag), and is well suited for the study of galaxy mergers, galaxy groups, and the low redshift (z<0.25) galaxy population. DR4 includes 32 value-added tables or Data Management Units (DMUs) that provide a number of measured and derived data products including GALEX, ESO KiDS, ESO VIKING, WISE and Herschel Space Observatory imaging. Within this release, we provide visual morphologies for 15330 galaxies to z<0.08, photometric redshift estimates for all 18million objects to r_KIDS~25mag, and stellar velocity dispersions for 111830 galaxies. We conclude by deriving the total galaxy stellar mass function (GSMF) and its sub-division by morphological class (elliptical, compact-bulge and disc, diffuse-bulge and disc, and disc only). This extends our previous measurement of the total GSMF down to 10^6.75 M_sol h^-2_70 and we find a total stellar mass density of rho_*=(2.97+/-0.04)x10^8 M_sol h_70 Mpc^-3 or Omega_*=(2.17+/-0.03)x10^-3 h^-1_70. We conclude that at z<0.1, the Universe has converted 4.9+/-0.1 per cent of the baryonic mass implied by Big Bang Nucleosynthesis into stars that are gravitationally bound within the galaxy population.

Understanding the connection between nuclear activity and galaxy environment remains critical in constraining models of galaxy evolution. By exploiting extensive catalogued data from the Galaxy and Mass Assembly (GAMA) survey, we identify a representative sample of 205 quasars at 0.1 < z < 0.35 and establish a comparison sample of galaxies, closely matched to the quasar sample in terms of both stellar mass and redshift. On scales <1 Mpc, the galaxy number counts and group membership of quasars appear entirely consistent with those of the matched galaxy sample. Despite this, we find that quasars are 1.5 times more likely to be classified as the group center, indicating a potential link between quasar activity and cold gas flows or galaxy interactions associated with rich group environments. On scales of a few Mpc, the clustering strength of both samples are statistically consistent and beyond 10 Mpc we find no evidence that quasars trace large scale structures any more than the galaxy control sample. Both populations are found to prefer intermediate-density sheets and filaments to either very high- or very low- density environments. This weak dependence of quasar activity on galaxy environment supports a paradigm in which quasars represent a phase in the lifetime of all massive galaxies and in which secular processes and a group-centric location are the dominant trigger of quasars at low redshift.

ABSTRACT In this study, we present a new experimental design using clustering-based redshift inference to measure the evolving galaxy luminosity function (GLF) spanning 5.5 decades from L ∼ 1011.5 to 106 L⊙. We use data from the Galaxy And Mass Assembly (GAMA) survey and the Kilo-Degree Survey (KiDS). We derive redshift distributions in bins of apparent magnitude to the limits of the GAMA-KiDS photometric catalogue: mr ≲ 23; more than a decade in luminosity beyond the limits of the GAMA spectroscopic redshift sample via clustering-based redshift inference. This technique uses spatial cross-correlation statistics for a reference set with known redshifts (in our case, the main GAMA sample) to derive the redshift distribution for the target ensemble. For the calibration of the redshift distribution, we use a simple parametrization with an adaptive normalization factor over the interval 0.005 < z < 0.48 to derive the clustering redshift results. We find that the GLF has a relatively constant power-law slope α ≈ −1.2 for −17 ≲ Mr ≲ −13, and then appears to steepen sharply for −13 ≲ Mr ≲ −10. This upturn appears to be where globular clusters (GCs) take over to dominate the source counts as a function of luminosity. Thus, we have mapped the GLF across the full range of the z ∼ 0 field galaxy population from the most luminous galaxies down to the GC scale.

ABSTRACT Relatively few X-ray sources are known that have low-mass galaxies as hosts. This is an important restriction on studies of active galactic nuclei (AGNs), hence black holes, and of X-ray binaries (XRBs) in low-mass galaxies; addressing it requires very large samples of both galaxies and X-ray sources. Here, we have matched the X-ray point sources found in the XXL-N field of the XXL survey (with an X-ray flux limit of ∼6 × 10−15 erg s−1 cm−2 in the [0.5–2] keV band) to galaxies with redshifts from the Galaxy And Mass Assembly (GAMA) G02 survey field (down to a magnitude limit r = 19.8) in order to search for AGNs and XRBs in GAMA galaxies, particularly those of low optical luminosity or stellar mass (fainter than Mr = −19 or $M_* \lesssim 10^{9.5}\, \mathrm{M}_{\odot }$). Out of a total of 1200 low-mass galaxies in the overlap region, we find a total of 28 potential X-ray source hosts, though this includes possible background contaminants. From a combination of photometry (optical and infrared colours), positional information, and optical spectra, we deduce that most of the ≃20 X-ray sources genuinely in low-mass galaxies are high-mass X-ray binaries in star-forming galaxies. None of the matched sources in a low-mass galaxy has a BPT classification as an AGN, and even ignoring this requirement, none passes both criteria of close match between the X-ray source position and optical galaxy centre (separation ≤3 arcsec) and high [O iii] line luminosity (above 1040.3 erg s−1).

Low-surface-brightness galaxies (LSBGs) – defined as systems that are fainter than the surface-brightness limits of past wide-area surveys – form the overwhelming majority of galaxies in the dwarf regime (M⋆ < 109 M⊙). Using NewHorizon, a high-resolution cosmological simulation, we study the origin of LSBGs and explain why LSBGs at similar stellar mass show the large observed spread in surface brightness. NewHorizon galaxies populate a well-defined locus in the surface brightness–stellar mass plane, with a spread of ∼3 mag arcsec−2, in agreement with deep Sloan Digital Sky Survey (SDSS) Stripe 82 data. Galaxies with fainter surface brightnesses today are born in regions of higher dark matter density. This results in faster gas accretion and more intense star formation at early epochs. The stronger resultant supernova feedback flattens gas profiles at a faster rate, which, in turn, creates shallower stellar profiles (i.e. more diffuse systems) more rapidly. As star formation declines towards late epochs ( z < 1), the larger tidal perturbations and ram pressure experienced by these systems (due to their denser local environments) accelerate the divergence in surface brightness, by increasing their effective radii and reducing star formation, respectively. A small minority of dwarfs depart from the main locus towards high surface brightnesses, making them detectable in past wide surveys (e.g. standard-depth SDSS images). These systems have anomalously high star formation rates, triggered by recent fly-by or merger-driven starbursts. We note that objects considered extreme or anomalous at the depth of current data sets, e.g. ‘ultra-diffuse galaxies’, actually dominate the predicted dwarf population and will be routinely visible in future surveys like the Legacy Survey of Space and Time (LSST).

ABSTRACT The discrepancy between estimates of the Hubble constant (H0) measured from local (z ≲ 0.1) scales and from scales of the sound horizon is a crucial problem in modern cosmology. Peculiar velocities (vpec) of standard candle distance indicators can systematically affect local H0 measurements. We here use 2MRS galaxies to measure the local galaxy density field, finding a notable z < 0.05 underdensity in the SGC-6dFGS region of 27 ± 2 per cent. However, no strong evidence for a ‘Local Void’ pertaining to the full 2MRS sky coverage is found. Galaxy densities are used to measure a density parameter, Δϕ+−, which we introduce as a proxy for vpec that quantifies density gradients along a supernova (SN) line of sight. Δϕ+− is found to correlate with local H0 estimates from 88 Pantheon Type Ia supernovae (SNe Ia; 0.02 < z < 0.05). Density structures on scales of ∼50 Mpc are found to correlate strongest with H0 estimates in both the observational data and in mock data from the MDPL2-Galacticus simulation. Using trends of H0 with Δϕ+−, we can correct for the effects of density structure on local H0 estimates, even in the presence of biased vpec. However, the difference in the inferred H0 estimate with and without the peculiar velocity correction is limited to < 0.1 per cent. We conclude that accounting for environmentally induced peculiar velocities of SN Ia host galaxies does not resolve the tension between local and CMB-derived H0 estimates.

ABSTRACT The size–mass galaxy distribution is a key diagnostic for galaxy evolution. Massive compact galaxies are potential surviving relics of a high-redshift phase of star formation. Some of these could be nearly unresolved in Sloan Digital Sky Survey (SDSS) imaging and thus not included in galaxy samples. To overcome this, a sample was selected from the combination of SDSS and UKIRT Infrared Deep Sky Survey (UKIDSS) photometry to r < 17.8. This was done using colour–colour selection, and then by obtaining accurate photometric redshifts (photo-z) using scaled flux matching (SFM). Compared to spectroscopic redshifts (spec-z), SFM obtained a 1σ scatter of 0.0125 with only 0.3 per cent outliers (|Δln (1 + z)| > 0.06). A sample of 163 186 galaxies was obtained with 0.04 < z < 0.15 over $2300\, {\rm deg}^2$ using a combination of spec-z and photo-z. Following Barro et al. log Σ1.5 = log M* − 1.5log r50, maj was used to define compactness. The spectroscopic completeness was 76 per cent for compact galaxies (log Σ1.5 > 10.5) compared to 92 per cent for normal-sized galaxies. This difference is primarily attributed to SDSS ‘fibre collisions’ and not the completeness of the main galaxy sample selection. Using environmental overdensities, this confirms that compact quiescent galaxies are significantly more likely to be found in high-density environments compared to normal-sized galaxies. By comparison with a high-redshift sample from 3D-HST, log Σ1.5 distribution functions show significant evolution, with this being a compelling way to compare with simulations such as EAGLE. The number density of compact quiescent galaxies drops by a factor of about 30 from z ∼ 2 to log (n/Mpc−3) = − 5.3 ± 0.4 in the SDSS–UKIDSS sample. The uncertainty is dominated by the steep cut off in log Σ1.5, which is demonstrated conclusively using this complete sample.

We estimate the intracluster light (ICL) component within a sample of 18 clusters detected in the XMM Cluster Survey (XCS) data using the deep (similar to 26.8 mag) Hyper Suprime-Cam Subaru Strategic Programme data release 1 i-band data. We apply a rest-frame mu(B) = 25 mag arcsec-2 isophotal threshold to our clusters, below which we define light as the ICL within an aperture of R-X,R-500 (X-ray estimate of R-500) centred on the brightest cluster galaxy (BCG). After applying careful masking and corrections for flux losses from background subtraction, we recover similar to 20 per cent of the ICL flux, approximately four times our estimate of the typical background at the same isophotal level (similar to 5 per cent). We find that the ICL makes up about similar to 24 per cent of the total cluster stellar mass on average (similar to 41 per cent including the flux contained in the BCG within 50 kpc); this value is well matched with other observational studies and semi-analytic/numerical simulations, but is significantly smaller than results from recent hydrodynamical simulations (even when measured in an observationally consistent way). We find no evidence for any links between the amount of ICL flux with cluster mass, but find a growth rate of 2-4 for the ICL between 0.1 < z < 0.5. We conclude that the ICL is the dominant evolutionary component of stellar mass in clusters from z similar to 1. Our work highlights the need for a consistent approach when measuring ICL alongside the need for deeper imaging, in order to unambiguously measure the ICL across as broad a redshift range as possible (e.g. 10-yr stacked imaging from the Vera C. Rubin Observatory).

The colour bimodality of galaxies provides an empirical basis for theories of galaxy evolution. However, the balance of processes that begets this bimodality has not yet been constrained. A more detailed view of the galaxy population is needed, which we achieve in this paper by using unsupervised machine learning to combine multidimensional data at two different epochs. We aim to understand the cosmic evolution of galaxy subpopulations by uncovering substructures within the colour bimodality. We choose a clustering algorithm that models clusters using only the most discriminative data available, and apply it to two galaxy samples: one from the second edition of the GALEX-SDSS-WISE Legacy Catalogue (GSWLC-2; z ∼ 0.06), and the other from the VIMOS Public Extragalactic Redshift Survey (VIPERS; z ∼ 0.65). We cluster within a nine-dimensional feature space defined purely by rest-frame ultraviolet-through-near-infrared colours. Both samples are similarly partitioned into seven clusters, breaking down into four of mostly star-forming galaxies (including the vast majority of green valley galaxies) and three of mostly passive galaxies. The separation between these two families of clusters suggests differences in the evolution of their galaxies, and that these differences are strongly expressed in their colours alone. The samples are closely related, with star-forming/green-valley clusters at both epochs forming morphological sequences, capturing the gradual internally driven growth of galaxy bulges. At high stellar masses, this growth is linked with quenching. However, it is only in our low-redshift sample that additional, environmental processes appear to be involved in the evolution of low-mass passive galaxies.

W illiam S.Burgett,M ichaelM .Vick,David S.Davis,M atthew Colless, Roberto DePropris,Ivan Baldry,Carlton Baugh,JossBland-Hawthorn, Terry Bridges,RussellCannon,Shaun Cole,ChrisCollins,W arrick Couch, NicholasCross,Gavin Dalton,Sim on Driver,GeorgeEfstathiou, Richard Ellis,CarlosS.Frenk,KarlGlazebrook,Edward Hawkins, CaroleJackson,OferLahav,Ian Lewis,StuartLum sden,SteveM addox, Darren M adgwick,PederNorberg,John A.Peacock,W illPercival, BrucePeterson,W illSutherland,and Keith Taylor Institute for A stronom y,U niversity ofH awaii,2680 W oodlawn D r.,H onolulu,H I 96822,U SA ; em ail:burgett@ ifa.hawaii.edu D epartm entofPhysics,U niversity ofTexas atD allas,Richardson,TX 75083-0688,U SA JointCenter for A strophysics,D ept.ofPhysics,U M BC,Baltim ore,M D 21250 U SA Laboratory for H igh Energy A strophysics,N A SA G SFC,Code 662,G reenbeltM D 20771,U SA Anglo-Australian O bservatory,P.O .Box 296,Epping,N SW 2121,Australia Research SchoolofA stronom y & A strophysics,The Australian N ationalU niversity,W eston Creek,ACT 2611,Australia D epartm entofPhysics & A stronom y,Johns H opkins U niversity,Baltim ore M D 21218-2686,U SA D epartm entofPhysics,U niversity ofD urham ,South Road,D urham ,D H 1 3LE,U K A strophysics Research Institute,LiverpoolJohn M oores U niversity,Twelve Q uays H ouse,Birkenhead,L14 1LD ,U K D epartm entofA strophysics,U niversity ofN ew South W ales,Sydney,N SW 2052,Australia D epartm entofPhysics,U niversity ofO xford,K eble Road,O xford,O X 1 3R H ,U K Rutherford A ppleton Laboratory,Chilton,D idcot,O X 11 0Q X ,U K Institute ofA stronom y,U niversity ofCam bridge,M adingley Road,Cam bridge,CB3 0H A ,U K D epartm entofA stronom y,California Institute ofTechnology,Pasadena,CA 91125,U SA SchoolofPhysics & A stronom y,U niversity ofN ottingham ,N ottingham ,N G 7 2R D ,U K CSIRO Australia Telescope N ationalFacility,PO Box 76,Epping,N SW 1710,Australia D epartm entofPhysics,U niversity ofLeeds,W oodhouse Lane,Leeds,LS2 9JT,U K Lawrence Berkeley N ationalLaboratory,1 Cyclotron Rd.,Berkeley,CA 94720,U SA ETH Z Institutfur A stronom ie,H PF G 3.1,ETH H onggerberg,CH -8093,Zurich,Switzerland Institute for A stronom y,U niversity ofEdinburgh,RoyalO bservatory,Blackford H ill,Edinburgh,EH 9 3H J,U K Physics D epartm ent,Q ueen’s U niversity,K ingston,O N ,K 7L 3N 6,Canada

The level of star formation in elliptical galaxies is poorly constrained, due to difficulties in quantifying the contamination of flux-based estimates of star formation from unrelated phenomena, such as AGN and old stellar populations. We here utilise core-collapse supernovae (CCSNe) as unambiguous tracers of recent star formation in ellipticals within a cosmic volume. We firstly isolate a sample of 421 z < 0.2, r < 21.8 mag CCSNe from the SDSS-II Supernova Survey. We then introduce a Bayesian method of identifying ellipticals via their colours and morphologies in a manner unbiased by redshift and yet consistent with manual classification from Galaxy Zoo 1. We find 25 of z < 0.2 r < 20 mag galaxies in the Stripe 82 region are ellipticals ( 28000 galaxies). In total, 36 CCSNe are found to reside in ellipticals. We demonstrate that such early-types contribute a non-negligible fraction of star formation to the present-day cosmic budget, at 11.2 ± 3.1 (stat) ^+3.0_-4.2 (sys) function of ellipticals, the mean specific star formation rate (SSFR; S) of these systems is derived. The best-fit slope is given by log (S(M)/yr) = - (0.80 ± 0.59) log (M/10^10.5M_⊙) - 10.83 ± 0.18. The mean SSFR for all log (M/M_⊙) > 10.0 ellipticals is found to be S = 9.2 ± 2.4 (stat) ^+2.7_-2.3 (sys) × 10^-12 yr^-1, which is consistent with recent estimates via SED-fitting, and is 11.8 ± 3.7 (stat) ^+3.5_-2.9 (sys) mean SSFR level on the main sequence as also derived from CCSNe. We find the median optical spectrum of elliptical CCSN hosts is statistically consistent with that of a control sample of ellipticals that do not host CCSNe, implying that these SN-derived results are well-representative of the total low-z elliptical population.