Abstract
We present the detection of 89 low surface brightness (LSB), and thus low stellar density galaxy candidates in the Perseus cluster core, of the kind named ‘ultra-diffuse galaxies’, with mean ...effective V-band surface brightnesses 24.8–27.1 mag arcsec−2, total V-band magnitudes −11.8 to −15.5 mag, and half-light radii 0.7–4.1 kpc. The candidates have been identified in a deep mosaic covering 0.3 deg2, based on wide-field imaging data obtained with the William Herschel Telescope. We find that the LSB galaxy population is depleted in the cluster centre and only very few LSB candidates have half-light radii larger than 3 kpc. This appears consistent with an estimate of their tidal radius, which does not reach beyond the stellar extent even if we assume a high dark matter content (M/L = 100). In fact, three of our candidates seem to be associated with tidal streams, which points to their current disruption. Given that published data on faint LSB candidates in the Coma cluster – with its comparable central density to Perseus – show the same dearth of large objects in the core region, we conclude that these cannot survive the strong tides in the centres of massive clusters.
We characterize the mass-dependent evolution of more than 8000 galaxies using spectroscopic redshifts from the DEEP2 Galaxy Redshift Survey in the range 0.4 < z < 1.4 and stellar masses calculated ...from K-band photometry obtained at Palomar Observatory. This sample spans more than 1.5 deg super(2) in four independent fields. Using rest-frame U - B color and O II equivalent widths, we distinguish star-forming from passive populations in order to explore the nature of "downsizing"--a pattern in which the sites of active star formation shift from high-mass galaxies at early times to lower mass systems at later epochs. We identify a mass limit, M sub(Q), above which star formation appears to be quenched and show that the physical mechanisms responsible for downsizing can thus be empirically quantified by charting the evolution in this threshold mass. We find that M sub(Q) decreases with time by a factor of 63 across our redshift range according to M sub(Q) 8(1 + z) super(3.5). To further constrain possible quenching mechanisms, we investigate how downsizing depends on local galaxy environment using the projected third-nearest-neighbor statistic D sub(p,3). For the majority of galaxies near the median density, there is no significant correlation between downsizing and environment. However, a trend is observed in the comparison between environments that are more than 3 times overdense or underdense relative to the median. Here, downsizing appears accelerated in overdense regions that host higher numbers of massive, early-type galaxies as compared to the underdense regions. Our results significantly constrain recent suggestions for the origin of downsizing and indicate that the process for quenching star formation must, primarily, be internally driven.
Abstract
We report the discovery of four galaxy candidates observed 450–600 Myr after the Big Bang with photometric redshifts between
z
∼ 8.3 and 10.2 measured using James Webb Space Telescope (JWST) ...NIRCam imaging of the galaxy cluster WHL0137−08 observed in eight filters spanning 0.8–5.0
μ
m, plus nine Hubble Space Telescope filters spanning 0.4–1.7
μ
m. One candidate is gravitationally lensed with a magnification of
μ
∼ 8, while the other three are located in a nearby NIRCam module with expected magnifications of
μ
≲ 1.1. Using SED fitting, we estimate the stellar masses of these galaxies are typically in the range
log
M
⋆
/
M
⊙
= 8.3–8.7. All appear young, with mass-weighted ages <240 Myr, low dust content
A
V
< 0.15 mag, and specific star formation rates sSFR ∼0.25–10 Gyr
−1
for most. One
z
∼ 9 candidate is consistent with an age <5 Myr and an sSFR ∼10 Gyr
−1
, as inferred from a strong F444W excess, implying O
iii
+H
β
rest-frame equivalent width ∼2000 Å, although an older
z
∼ 10 object is also allowed. Another
z
∼ 9 candidate is lensed into an arc 2.″4 long with a magnification of
μ
∼ 8. This arc is the most spatially resolved galaxy at
z
∼ 9 known to date, revealing structures ∼30 pc across. Follow-up spectroscopy of WHL0137−08 with JWST/NIRSpec will be useful to spectroscopically confirm these high-redshift galaxy candidates and to study their physical properties in more detail.
ABSTRACTThis paper begins a series in which we examine the structures of distant galaxies to directly determine the history of their formation modes. We start this series by examining the structures ...of zF850LP < 27 galaxies in the Hubble Ultra-Deep Field (UDF), the deepest high-resolution optical image taken to date. We investigate a few basic features of galaxy structure using this image. These include: (1) the agreement of visual eye-ball classifications and non-parametric quantitative (CAS, Gini/M20) methods; (2) how distant galaxy quantitative structures can vary as a function of rest-frame wavelength; and (3) the evolution of distant galaxy structures up to z similar to 3. One of our major conclusions is that the majority of galaxies with z850 < 27 are peculiar in appearance, and that galaxy assembly is rapidly occurring at these magnitudes, even up to the present time. We find a general agreement between galaxy classification by eye and through quantitative methods, as well as a general agreement between the CAS and the Gini/M20 parameters. We find that the Gini/M20 method appears to find a larger number of galaxy mergers than the CAS system, but contains a larger contamination from non-mergers. We furthermore calculate the merger rate of galaxies in the UDF up to z similar to 3, finding an increase with redshift as well as stellar mass, confirming previous work in the Hubble Deep Field. We find that massive galaxies with M* > 1010Modot undergo 4.3-0.8+0.8 major galaxy mergers at z < 3, with all of this merging occurring at z > 1.
Submillimetre galaxies (SMGs) are among the most luminous dusty galaxies in the Universe, but their true nature remains unclear; are SMGs the progenitors of the massive elliptical galaxies we see in ...the local Universe, or are they just a short-lived phase among more typical star-forming galaxies? To explore this problem further, we investigate the clustering of SMGs identified in the SCUBA-2 Cosmology Legacy Survey. We use a catalogue of submillimetre (850 mu m) source identifications derived using a combination of radio counterparts and colour/infrared selection to analyse a sample of 610 SMG counterparts in the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Survey (UKIDSS) Ultra Deep Survey (UDS), making this the largest high-redshift sample of these galaxies to date. Using angular cross-correlation techniques, we estimate the halo masses for this large sample of SMGs and compare them with passive and star-forming galaxies selected in the same field. We find that SMGs, on average, occupy high-mass dark matter haloes ... at redshifts z > 2.5, consistent with being the progenitors of massive quiescent galaxies in present-day galaxy clusters. We also find evidence of downsizing, in which SMG activity shifts to lower mass haloes at lower redshifts. In terms of their clustering and halo masses, SMGs appear to be consistent with other star-forming galaxies at a given redshift. (ProQuest: ... denotes formulae/symbols omitted.)
Connecting galaxies with their descendants (or progenitors) at different redshifts can yield strong constraints on galaxy evolution. Observational studies have historically selected samples of ...galaxies using a physical quantity, such as stellar mass, either above a constant limit or at a constant cumulative number density. Investigation into the efficacy of these selection methods has not been fully explored. Using a set of four semi-analytical models based on the output of the Millennium Simulation, we find that selecting galaxies at a constant number density (in the range −4.3 < log n Mpc−3 h
3 < −3.0) is superior to a constant stellar mass selected sample, although it still has significant limitations. Recovery of the average stellar mass, stellar mass density and average star formation rate is highly dependent on the choice of number density but can all be recovered to within <50 per cent at the commonly employed choice of log n Mpc−3 h
3 = −4.0, corresponding to log M⊙ h
−1 ∼ 11.2 at z = 0, but this increases at lower mass limits. We show that there is a large scatter between the location of a given galaxy in a rank ordering based on stellar mass between different redshifts. We find that the inferred velocity dispersion may be a better tracer of galaxy properties, although further investigation is warranted into simulating this property. Finally, we find that over large redshift ranges selection at a constant number density is more effective in tracing the progenitors of modern galaxies than vice versa.
With the ever-growing popularity of integral field unit (IFU) spectroscopy, countless observations are being performed over multiple object systems such as blank fields and galaxy clusters. With ...this, an increasing amount of time is being spent extracting one-dimensional object spectra from large three-dimensional data cubes. However, a great deal of information available within these data cubes is overlooked in favor of photometrically based spatial information. Here we present a novel yet simple approach of optimal source identification utilizing the wealth of information available within an IFU data cube, rather than relying on ancillary imaging. Through the application of these techniques, we show that we are able to obtain object spectra comparable to deep photometry-weighted extractions without the need for ancillary imaging. Further, implementing our custom-designed algorithms can improve the signal-to-noise ratio of extracted spectra and successfully deblend sources from nearby contaminants. This will be a critical tool for future IFU observations of blank and deep fields, especially over large areas where automation is necessary. We implement these techniques in the Python-based spectral extraction software, AutoSpec, which is available via GitHub at https://github.com/a-griffiths/AutoSpec and Zenodo at https://doi.org/10.5281/zenodo.1305848.
We measure the mass functions for generically red and blue galaxies, using a z < 0.12 sample of log M* > 8.7 field galaxies from the Galaxy And Mass Assembly (GAMA) survey. Our motivation is that, as ...we show, the dominant uncertainty in existing measurements stems from how 'red' and 'blue' galaxies have been selected/defined. Accordingly, we model our data as two naturally overlapping populations, each with their own mass function and colour-mass relation, which enables us characterize the two populations without having to specify a priori which galaxies are 'red' and 'blue'. Our results then provide the means to derive objective operational definitions for the terms 'red' and 'blue', which are based on the phenomenology of the colour-mass diagrams. Informed by this descriptive modelling, we show that (1) after accounting for dust, the stellar colours of 'blue' galaxies do not depend strongly on mass; (2) the tight, flat 'dead sequence' does not extend much below log M* ~ 10.5; instead, (3) the stellar colours of 'red' galaxies vary rather strongly with mass, such that lower mass 'red' galaxies have bluer stellar populations; (4) below log M* ~ 9.3, the 'red' population dissolves into obscurity, and it becomes problematic to talk about two distinct populations; as a consequence, (5) it is hard to meaningfully constrain the shape, including the existence of an upturn, of the 'red' galaxy mass function below log M* ~ 9.3. Points 1-4 provide meaningful targets for models of galaxy formation and evolution to aim for.
ABSTRACT
Many aspects concerning the formation of spiral and disc galaxies remain unresolved, despite their discovery and detailed study over the past 150 yr. As such, we present the results of an ...observational search for proto-spiral galaxies and their earliest formation, including the discovery of a significant population of spiral-like and clumpy galaxies at z > 1 in deep Hubble Space Telescope CANDELS imaging. We carry out a detailed analysis of this population, characterizing their number density evolution, masses, star formation rates (SFR), and sizes. Overall, we find a surprisingly high overall number density of massive $M_{*} \gt 10^{10}\, \mathrm{M}_{\odot }$ spiral-like galaxies (including clumpy spirals) at z > 1 of $0.18\, {\rm per}\, \mathrm{arcmin}^{-2}$. We measure and characterize the decline in the number of these systems at higher redshift using simulations to correct for redshift effects in identifications, finding that the true fraction of spiral-like galaxies grows at lower redshifts as ∼ (1 + z)−1.1. This is such that the absolute numbers of spirals increases by a factor of ∼10 between z = 2.5 and z = 0.5. We also demonstrate that these spiral-like systems have large sizes at z > 2, and high SFRs, above the main-sequence, These galaxies represent a major mode of galaxy formation in the early Universe, perhaps driven by the spiral structure itself. We finally discuss the origin of these systems, including their likely formation through gas accretion and minor mergers, but conclude that major mergers are an unlikely cause.
Using a sample of 425 nearby brightest cluster galaxies (BCGs) from von der Linden et al., we study the relationship between their internal properties (stellar masses, structural parameters and ...morphologies) and their environment. More massive BCGs tend to inhabit denser regions and more massive clusters than lower mass BCGs. Furthermore, cDs, which are BCGs with particularly extended envelopes, seem to prefer marginally denser regions and tend to be hosted by more massive haloes than elliptical BCGs. cD and elliptical BCGs show parallel positive correlations between their stellar masses and environmental densities. However, at a fixed environmental density, cDs are, on average, ∼40 per cent more massive. Our results, together with the findings of previous studies, suggest an evolutionary link between elliptical and cD BCGs. We suggest that most present-day cDs started their life as ellipticals, which subsequently grew in stellar mass and size due to mergers. In this process, the cD envelope developed. The large scatter in the stellar masses and sizes of the cDs reflects their different merger histories. The growth of the BCGs in mass and size seems to be linked to the hierarchical growth of the structures they inhabit: as the groups and clusters became denser and more massive, the BCGs at their centres also grew. This process is nearing completion since the majority (∼60 per cent) of the BCGs in the local Universe have cD morphology. However, the presence of galaxies with intermediate morphological classes (between ellipticals and cDs) suggests that the growth and morphological transformation of some BCGs is still ongoing.
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