We present a kinematic study of the outer regions (R_25<R<2 R_25) of 17 edge-on disk galaxies. Using deep long-slit spectroscopy (flux sensitivity a few 10^-19 erg s^-1 cm^-2 arcsec^-2), we search ...for H-alpha emission, which must be emitted at these flux levels by any accumulation of hydrogen due to the presence of the extragalactic UV background and any other, local source of UV flux. We present results from the individual galaxy spectra and a stacked composite. We detect H-alpha in many cases well beyond R_25 and sometimes as far as 2 R_25. The combination of sensitivity, spatial resolution, and kinematic resolution of this technique thus provides a powerful complement to 21-cm observations. Kinematics in the outer disk are generally disk-like (flat rotation curves, small velocity dispersions) at all radii, and there is no evidence for a change in the velocity dispersion with radius. We place strong limits, few percent, on the existence of counter-rotating gas out to 1.5 R_25. These results suggest that thin disks extend well beyond R_25; however, we also find a few puzzling anomalies. In ESO 323-G033 we find two emission regions that have velocities close to the systemic velocity rather than the expected rotation velocity. These low relative velocities are unlikely to be simply due to projection effects and so suggest that these regions are not on disk-plane, circular orbits. In MCG-01-31-002 we find emission from gas with a large velocity dispersion that is co-rotating with the inner disk.
We present a map of the total intrinsic reddening across ~34 deg\(^{2}\) of the Small Magellanic Cloud (SMC) derived using optical (\(ugriz\)) and near-infrared (IR; \(YJK_{\mathrm{s}}\)) spectral ...energy distributions (SEDs) of background galaxies. The reddening map is created using a subsample of 29,274 galaxies with low levels of intrinsic reddening based on the LePhare \(\chi^{2}\) minimisation SED-fitting routine. We find statistically significant enhanced levels of reddening associated with the main body of the SMC compared with regions in the outskirts \(\Delta E(B-V)\simeq 0.3\) mag. A comparison with literature reddening maps of the SMC shows that, after correcting for differences in the volume of the SMC sampled, there is good agreement between our results and maps created using young stars. In contrast, we find significant discrepancies between our results and maps created using old stars or based on longer wavelength far-IR dust emission that could stem from biased samples in the former and uncertainties in the far-IR emissivity and the optical properties of the dust grains in the latter. This study represents one of the first large-scale categorisations of extragalactic sources behind the SMC and as such we provide the LePhare outputs for our full sample of ~500,000 sources.
We study the star formation histories (SFHs) and mass-weighted ages of 331 UVJ-selected quiescent galaxies in 11 galaxy clusters and in the field at 1<z<1.5 from the Gemini Observations of Galaxies ...in Rich Early ENvironments (GOGREEN) survey. We determine the SFHs of individual galaxies by simultaneously fitting rest-frame optical spectroscopy and broadband photometry to stellar population models. We confirm that the SFHs are consistent with more massive galaxies having on average earlier formation times. Comparing galaxies found in massive clusters with those in the field, we find galaxies with \(M_\ast<10^{11.3}\) M\(_{\odot}\) in the field have more extended SFHs. From the SFHs we calculate the mass-weighted ages, and compare age distributions of galaxies between the two environments, at fixed mass. We constrain the difference in mass-weighted ages between field and cluster galaxies to \(0.31_{^{-0.33}}^{_{+0.51}}\) Gyr, in the sense that cluster galaxies are older. We place this result in the context of two simple quenching models and show that neither environmental quenching based on time since infall (without pre-processing) nor a difference in formation times alone can reproduce both the average age difference and relative quenched fractions. This is distinctly different from local clusters, for which the majority of the quenched population is consistent with having been environmentally quenched upon infall. Our results suggest that quenched population in galaxy clusters at z>1 has been driven by different physical processes than those at play at z=0.
We present a detailed reconstruction of the star-formation history of the Constellation III region in the Large Magellanic Cloud, to constrain the formation mechanism of this enigmatic feature. Star ...formation in Constellation III seems to have taken place during two distinct epochs: there is the 8-15 Myr epoch that had previously been recognized, but we also see strong evidence for a separate "burst" of star formation 25-30 Myr ago. The "super-supernova" or GRB blast wave model for the formation of Constellation III is difficult to reconcile with such an extended, two-epoch star formation history, because the shock wave should have induced star formation throughout the structure simultaneously, and any unconsumed gas would quickly be dissipated, leaving nothing from which to form a subsequent burst of activity. We propose a "truly stochastic" self-propagating star formation model, distinct from the canonical model in which star formation proceeds in a radially-directed wave from the center of Constellation III to its perimeter. As others have noted, and we now confirm, the bulk age gradients demanded by such a model are simply not present in Constellation III. In our scenario, the prestellar gas is somehow pushed into these large-scale arc structures, without simultaneously triggering immediate and violent star formation throughout the structure. Rather, star formation proceeds in the arc according to the local physical conditions of the gas. Self-propagating star formation is certainly possible, but in a truly stochastic manner, without a directed, large scale pattern.
We present results on the environmental dependence of the star-forming galaxy
main sequence in 11 galaxy cluster fields at $1.0 < z < 1.5$ from the Gemini
Observations of Galaxies in Rich Early ...Environments Survey (GOGREEN) survey. We
use a homogeneously selected sample of field and cluster galaxies whose
membership is derived from dynamical analysis. Using OII-derived star
formation rates (SFRs), we find that cluster galaxies have suppressed SFRs at
fixed stellar mass in comparison to their field counterparts by a factor of 1.4
$\pm$ 0.1 ($\sim3.3\sigma$) across the stellar mass range: $9.0 < \log(M_{*}
/M_{\odot}) < 11.2$. We also find that this modest suppression in the cluster
galaxy star-forming main sequence is mass and redshift dependent: the
difference between cluster and field increases towards lower stellar masses and
lower redshift. When comparing the distribution of cluster and field galaxy
SFRs to the star-forming main sequence, we find an overall shift towards lower
SFRs in the cluster population, and note the absence of a tail of high SFR
galaxies as seen in the field. Given this observed suppression in the cluster
galaxy star-forming main sequence, we explore the implications for several
scenarios such as formation time differences between cluster and field
galaxies, and environmentally-induced star formation quenching and associated
timescales.
The distribution of satellite galaxies Lorrimer, Stephen J.; Frenk, Carlos S.; Smith, Rodney M. ...
Monthly notices of the Royal Astronomical Society,
08/1994, Volume:
269, Issue:
3
Journal Article
Peer reviewed
We carry out a statistical analysis of the distribution of faint satellites around galaxies of differing Hubble type. Following Holmberg, we count the number of faint images on Schmidt survey plates ...around primaries of known redshift. Our procedure leads to a highly significant detection of the satellites. On average, the projected distance of these systems from their primaries is distributed as $\sum (r_p)\propto r^{-\gamma}_\text p$ with gamma γ ∼ 0.9. The satellite populations around primaries of different Hubble type are significantly different: satellites are more concentrated around early-type primaries, with a higher absolute abundance within ∼ 0.25h–1 Mpc1. If we assume a standard ‘field’ luminosity function, we find that galaxies with – 18 < B < – 172 are about three times more weakly clustered to their primaries than are bright galaxies at separations of order 1 Mpc. At fainter magnitudes, the clustering appears stronger, suggesting the presence of a new population of dwarfs which exist only in close association with bright galaxies.
We present a method to map the total intrinsic reddening of a foreground extinguishing medium via the analysis of spectral energy distributions (SEDs) of background galaxies. In this pilot study, we ...implement this technique in two distinct regions of the Small Magellanic Cloud (SMC) - the bar and the southern outskirts - using a combination of optical and near-infrared \(ugrizYJK_{\mathrm{s}}\) broadband imaging. We adopt the LePhare \(\chi^{2}\)-minimisation SED-fitting routine and various samples of galaxies and/or quasi-stellar objects to investigate the intrinsic reddening. We find that only when we construct reddening maps using objects classified as galaxies with low levels of intrinsic reddening (i.e. ellipticals/lenticulars and early-type spirals), the resultant maps are consistent with previous literature determinations i.e. the intrinsic reddening of the SMC bar is higher than that in the outer environs. We employ two sets of galaxy templates - one theoretical and one empirical - to test for template dependencies in the resulting reddening maps and find that the theoretical templates imply systematically higher reddening values by up to 0.20 mag in \(E(B-V)\). A comparison with previous reddening maps, based on the stellar components of the SMC, typically shows reasonable agreement. There is, however, significant variation amongst the literature reddening maps as to the level of intrinsic reddening associated with the bar. Thus, it is difficult to unambiguously state that instances of significant discrepancies are the result of appreciable levels of dust not accounted for in some literature reddening maps or whether they reflect issues with our adopted methodology.
The periphery of the Small Magellanic Cloud (SMC) can unlock important information regarding galaxy formation and evolution in interacting systems. Here, we present a detailed study of the extended ...stellar structure of the SMC using deep colour-magnitude diagrams (CMDs), obtained as part of the Survey of the MAgellanic Stellar History (SMASH). Special care was taken in the decontamination of our data from MW foreground stars, including from foreground globular clusters NGC 362 and 47 Tuc. We derived the SMC surface brightness using a ``conservative'' approach from which we calculated the general parameters of the SMC, finding a staggered surface brightness profile. We also traced the fainter outskirts by constructing a stellar density profile. This approach, based on stellar counts of the oldest main sequence turn-off (MSTO) stars, uncovered a tidally disrupted stellar feature that reaches as far out as 12 degrees from the SMC centre. We also serendipitously found a faint feature of unknown origin located at \(\sim 14\) degrees from the centre of the SMC and that we tentatively associated to a more distant structure. We compared our results to in-house simulations of a \(1\times10^{9} M_\odot\) SMC, finding that its elliptical shape can be explained by its tidal disruption under the combined presence of the MW and the LMC. Finally, we found that the older stellar populations show a smooth profile while the younger component presents a jump in the density followed by a flat profile, confirming the heavily disturbed nature of the SMC.
The observed flat rotation curves of galaxies require either the presence of dark matter in Newtonian gravitational potentials or a significant modification to the theory of gravity at galactic ...scales. Detecting relativistic Doppler shifts and gravitational effects in the rotation curves offers a tool for distinguishing between predictions of gravity theories that modify the inertia of particles and those that modify the field equations. These higher-order effects also allow us in principle, to test whether dark matter particles obey the equivalence principle. We calculate here the magnitudes of the relativistic Doppler and gravitational shifts expected in realistic models of galaxies in a general metric theory of gravity. We identify a number of observable quantities that measure independently the special- and general-relativistic effects in each galaxy and suggest that both effects might be detected in a statistical sense by combining appropriately the rotation curves of a large number of galaxies.
We present \(BVI\) surface photometry of 31 dwarf galaxy candidates discovered in a deep image stack from the KMTNet Supernova Program of \(\sim\) 30 square degrees centered on the nearby NGC 2784 ...galaxy group. Our final images have a 3\(\sigma\) surface brightness detection limit of \(\mu_V\approx 28.5\) mag arcsec\(^{-2}\). The faintest central surface brightness that we measure is \(\mu_{0,V} = 26.1\) mag arcsec\(^{-2}\). If these candidates are at the distance of NGC 2784, then they have absolute magnitudes greater than \(M_V = -9.5\) mag and effective radii larger than 170 pc. Their radial number density decreases exponentially with distance from the center of NGC 2784 until it flattens beyond a radius of 0.5 Mpc. We interpret the baseline density level to represent the background contamination and so estimate that 22 of the 31 new candidates are dwarf members of the group. The candidate's average color, \(\langle (B-V)_0\rangle\approx 0.7\), and Sersic structural parameters are consistent with those parameters for the dwarf populations of other groups. We find that the central population of dwarfs is redder and brighter than the rest of the population. The measured faint end slope of the luminosity function, \(\alpha\approx-1.33\), is steeper than that of the Local Group but consistent with published results for other groups. Such comparisons are complicated by systematic differences among different studies, but will be simpler when the KMTNet survey, which will provide homogenous data for 15 to 20 groups, is completed.
PDF