14 research outputs found
Kiloparsec-scale AGN outflows and feedback in merger-free galaxies
Recent observations and simulations have challenged the long-held paradigm that mergers are the dominant mechanism driving the growth of both galaxies and supermassive black holes (SMBH), in favour of non-merger (secular) processes. In this pilot study of merger-free SMBH and galaxy growth, we use Keck Cosmic Web Imager spectral observations to examine four low-redshift (0.043 < z < 0.073) disc-dominated âbulgelessâ galaxies hosting luminous active galactic nucleus (AGN), assumed to be merger-free. We detect blueshifted broadened [OâIII] emission from outflows in all four sources, which the [OIII]/HÎČ ratios reveal are ionized by the AGN. We calculate outflow rates in the range 0.12â0.7 Mâ yrâ1â , with velocities of 675â1710 km sâ1â , large radial extents of 0.6â2.4 kpcâ , and SMBH accretion rates of 0.02â0.07 Mâ yrâ1â . We find that the outflow rates, kinematics, and energy injection rates are typical of the wider population of low-redshift AGN, and have velocities exceeding the galaxy escape velocity by a factor of âŒ30, suggesting that these outflows will have a substantial impact through AGN feedback. Therefore, if both merger-driven and non-merger-driven SMBH growth lead to co-evolution, this suggests that co-evolution is regulated by feedback in both scenarios. Simulations find that bars and spiral arms can drive inflows to galactic centers at rates an order of magnitude larger than the combined SMBH accretion and outflow rates of our four targets. This work therefore provides further evidence that non-merger processes are sufficient to fuel SMBH growth and AGN outflows in disc galaxies
Galaxy Zoo DESI: Detailed Morphology Measurements for 8.7M Galaxies in the DESI Legacy Imaging Surveys
We present detailed morphology measurements for 8.67 million galaxies in the
DESI Legacy Imaging Surveys (DECaLS, MzLS, and BASS, plus DES). These are
automated measurements made by deep learning models trained on Galaxy Zoo
volunteer votes. Our models typically predict the fraction of volunteers
selecting each answer to within 5-10\% for every answer to every GZ question.
The models are trained on newly-collected votes for DESI-LS DR8 images as well
as historical votes from GZ DECaLS. We also release the newly-collected votes.
Extending our morphology measurements outside of the previously-released
DECaLS/SDSS intersection increases our sky coverage by a factor of 4 (5,000 to
19,000 deg) and allows for full overlap with complementary surveys
including ALFALFA and MaNGA.Comment: 20 pages. Accepted at MNRAS. Catalog available via
https://zenodo.org/record/7786416. Pretrained models available via
https://github.com/mwalmsley/zoobot. Vizier and Astro Data Lab access not yet
available. With thanks to the Galaxy Zoo volunteer
The most luminous, merger-free AGN show only marginal correlation with bar presence
The role of large-scale bars in the fuelling of active galactic nuclei (AGN)
is still debated, even as evidence mounts that black hole growth in the absence
of galaxy mergers cumulatively dominated and may substantially influence disc
(i.e., merger-free) galaxy evolution. We investigate whether large-scale
galactic bars are a good candidate for merger-free AGN fuelling. Specifically,
we combine slit spectroscopy and Hubble Space Telescope imagery to characterise
star formation rates (SFRs) and stellar masses of the unambiguously
disc-dominated host galaxies of a sample of luminous, Type-1 AGN with 0.02 < z
0.024. After carefully correcting for AGN signal, we find no clear difference
in SFR between AGN hosts and a stellar mass-matched sample of galaxies lacking
an AGN (0.013 < z < 0.19), although this could be due to a small sample size
(n_AGN = 34). We correct for SFR and stellar mass to minimise selection biases,
and compare the bar fraction in the two samples. We find that AGN are
marginally (1.7) more likely to host a bar than inactive galaxies, with
AGN hosts having a bar fraction, fbar = 0.59^{+0.08}_{-0.09} and inactive
galaxies having a bar fraction fbar = 0.44^{+0.08}_{-0.09}. However, we find no
further differences between SFR- and mass-matched AGN and inactive samples.
While bars could potentially trigger AGN activity, they appear to have no
further, unique effect on a galaxy's stellar mass or SFR.Comment: 15 pages (9 figures). Accepted for publication in MNRA
Quantifying the Poor Purity and Completeness of Morphological Samples Selected by Galaxy Colour
The galaxy population is strongly bimodal in both colour and morphology, and the two measures correlate strongly, with most blue galaxies being late-types (spirals) and most early-types, typically ellipticals, being red. This observation has led to the use of colour as a convenient selection criteria to make samples which are then labelled by morphology. Such use of colour as a proxy for morphology results in necessarily impure and incomplete samples. In this paper, we make use of the morphological labels produced by Galaxy Zoo to measure how incomplete and impure such samples are, considering optical (ugriz), NUV and NIR (JHK) bands. The best single colour optical selection is found using a threshold of g â r = 0.742, but this still results in a sample where only 56% of red galaxies are smooth and 56% of smooth galaxies are red. Use of the NUV gives some improvement over purely optical bands, particularly for late-types, but still results in low purity/completeness for early-types. No significant improvement is found by adding NIR bands. With any two bands, including NUV, a sample of early-types with greater than two-thirds purity cannot be constructed. Advances in quantitative galaxy morphologies have made colour-morphology proxy selections largely unnecessary going forward; where such assumptions are still required, we recommend studies carefully consider the implications of sample incompleteness/impurity
The most luminous, merger-free AGN show only marginal correlation with bar presence
The role of large-scale bars in the fuelling of active galactic nuclei (AGN) is still debated, even as evidence mounts that black hole growth in the absence of galaxy mergers cumulatively dominates and may substantially influence disc (i.e., merger-free) galaxy evolution. We investigate whether large-scale galactic bars are a good candidate for merger-free AGN fuelling. Specifically, we combine slit spectroscopy and Hubble Space Telescope imagery to characterise star formation rates (SFRs) and stellar masses of the unambiguously disc-dominated host galaxies of a sample of luminous, Type-1 AGN with 0.02 < < 0.24. After carefully correcting for AGN signal, we find no clear difference in SFR between AGN hosts and a stellar mass-matched sample of galaxies lacking an AGN (0.013 < < 0.19), although this could be due to small sample size (AGN = 34). We correct for SFR and stellar mass to minimise selection biases, and compare the bar fraction in the two samples. We find that AGN are marginally (⌠1.7Ï) more likely to host a bar than inactive galaxies, with AGN hosts having a bar fraction, bar = 0.59+0.08 â0.09 and inactive galaxies having a bar fraction, bar = 0.44+0.08 â0.09. However, we find no further differences between SFR- and mass-matched AGN and inactive samples. While bars could potentially trigger AGN activity, they appear to have no further, unique effect on a galaxyâs stellar mass or SF
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Galaxy Zoo DESI: Detailed morphology measurements for 8.7M galaxies in the DESI Legacy Imaging Surveys
We present detailed morphology measurements for 8.67 million galaxies in the DESI Legacy Imaging Surveys (DECaLS, MzLS, and BASS, plus DES). These are automated measurements made by deep learning models trained on Galaxy Zoo volunteer votes. Our models typically predict the fraction of volunteers selecting each answer to within 5â10% for every answer to every GZ question. The models are trained on newly-collected votes for DESI-LS DR8 images as well as historical votes from GZ DECaLS. We also release the newly-collected votes. Extending our morphology measurements outside of the previously-released DECaLS/SDSS intersection increases our sky coverage by a factor of 4 (5000 to 19 000 deg2) and allows for full overlap with complementary surveys including ALFALFA and MaNGA
Galaxy Zoo DESI : Detailed morphology measurements for 8.7M galaxies in the DESI Legacy Imaging Surveys
We present detailed morphology measurements for 8.67 million galaxies in the DESI Legacy Imaging Surveys (DECaLS, MzLS, and BASS, plus DES). These are automated measurements made by deep learning models trained on Galaxy Zoo volunteer votes. Our models typically predict the fraction of volunteers selecting each answer to within 5â10% for every answer to every GZ question. The models are trained on newly-collected votes for DESI-LS DR8 images as well as historical votes from GZ DECaLS. We also release the newly-collected votes. Extending our morphology measurements outside of the previously-released DECaLS/SDSS intersection increases our sky coverage by a factor of 4 (5000 to 19 000 deg2) and allows for full overlap with complementary surveys including ALFALFA and MaNGA
Gems of the Galaxy ZoosâA Wide-ranging Hubble Space Telescope Gap-filler Program*
We describe the Gems of the Galaxy Zoos (Zoo Gems) project, a gap-filler project using short windows in the Hubble Space Telescope's schedule. As with previous snapshot programs, targets are taken from a pool based on position; we combine objects selected by volunteers in both the Galaxy Zoo and Radio Galaxy Zoo citizen-science projects. Zoo Gems uses exposures with the Advanced Camera for Surveys to address a broad range of topics in galaxy morphology, interstellar-medium content, host galaxies of active galactic nuclei, and galaxy evolution. Science cases include studying galaxy interactions, backlit dust in galaxies, post-starburst systems, rings and peculiar spiral patterns, outliers from the usual colorâmorphology relation, Green Pea compact starburst systems, double radio sources with spiral host galaxies, and extended emission-line regions around active galactic nuclei. For many of these science categories, final selection of targets from a larger list used public input via a voting process. Highlights to date include the prevalence of tightly wound spiral structure in blue, apparently early-type galaxies, a nearly complete Einstein ring from a group lens, redder components at lower surface brightness surrounding compact Green Pea starbursts, and high-probability examples of spiral galaxies hosting large double radio sources