arXiv subjects

Richard S. Ellis

Publications and source records attributed to Richard S. Ellis.

At least 145 records · Page 8Linked to original sources

arXiv2011

The Assembly History of Disk Galaxies: I - The Tully-Fisher Relation to z~1.3 from Deep Exposures with DEIMOS

We present new measures of the evolving scaling relations between stellar mass, luminosity and rotational velocity for a morphologically-inclusive sample of 129 disk-like galaxies with z_AB<22.5 in the redshift range 0.2 ~1, with no significant evolution to ~0.3, \DeltaM_stellar ~ 0.04+/-0.07 dex. A clearer trend of evolution is seen in the B-band Tully-Fisher relation corresponding to a decline in luminosity of \DeltaM_B ~ 0.85+/-0.28 magnitudes at fixed velocity over the same redshift range, reflecting the changes in star formation over this period. As an illustration of the opportunities possible when gas masses are available for a sample such as ours, we show how our dynamical and stellar mass data can be used to evaluate the likely contributions of baryons and dark matter to the assembly history of spiral galaxies.

astro-ph.CO↗

arXiv2011

PTF10ops - a subluminous, normal-width lightcurve Type Ia supernova in the middle of nowhere

PTF10ops is a Type Ia supernova (SN Ia), whose lightcurve and spectral properties place it outside the current SN Ia subtype classifications. Its spectra display the characteristic lines of subluminous SNe Ia, but it has a normal-width lightcurve with a long rise-time, typical of normal luminosity SNe Ia. The early-time optical spectra of PTF10ops were modelled using a spectral fitting code and found to have all the lines typically seen in subluminous SNe Ia, without the need to invoke more uncommon elements. The host galaxy environment of PTF10ops is also unusual with no galaxy detected at the position of the SN down to an absolute limiting magnitude of r \geq -12.0 mag, but a very massive galaxy is present at a separation of ~148 kpc and at the same redshift as suggested by the SN spectral features. The progenitor of PTF10ops is most likely a very old star, possibly in a low metallicity environment, which affects its explosion mechanism and observational characteristics. PTF10ops does not easily fit into any of the current models of either subluminous or normal SN Ia progenitor channels.

astro-ph.SR↗

arXiv2011

Monte Carlo Methods for Rough Free Energy Landscapes: Population Annealing and Parallel Tempering

Parallel tempering and population annealing are both effective methods for simulating equilibrium systems with rough free energy landscapes. Parallel tempering, also known as replica exchange Monte Carlo, is a Markov chain Monte Carlo method while population annealing is a sequential Monte Carlo method. Both methods overcome the exponential slowing associated with high free energy barriers. The convergence properties and efficiency of the two methods are compared. For large systems, population annealing initially converges to equilibrium more rapidly than parallel tempering for the same amount of computational work. However, parallel tempering converges exponentially and population annealing inversely in the computational work so that ultimately parallel tempering approaches equilibrium more rapidly than population annealing.

cond-mat.stat-mech↗

arXiv2011

The Emission Line Properties of Gravitationally-lensed 1.5 < z < 5 Galaxies

We present and analyse near-infrared spectroscopy for a sample of 28 gravitationally- lensed star-forming galaxies in the redshift range 1.5 < z < 5, observed mostly with the Keck II telescope. With typical magnifications of ~1.5-4 magnitudes, our survey provides a valuable census of star formation rates, gas-phase metallicities and dynamical masses for a representative sample of low luminosity galaxies seen at a formative period in cosmic history. We find less evolution in the mass-metallicity relation compared to earlier work that focused on more luminous systems with z - 2-3, especially in the low mass (- 10^9 Msol) where our sample is - 0.25 dex more metal-rich. We interpret this offset as a result of the lower star formation rates (typically a factor of -10 lower) for a given stellar mass in our sub-luminous systems. Taking this effect into account, we conclude our objects are consistent with a fundamental metallicity relation recently proposed from unlensed observations.

astro-ph.CO↗

arXiv2011

The Dark Matter Distribution in Abell 383: Evidence for a Shallow Density Cusp from Improved Lensing, Stellar Kinematic and X-ray Data

We extend our analyses of the dark matter (DM) distribution in relaxed clusters to the case of Abell 383, a luminous X-ray cluster at z=0.189 with a dominant central galaxy and numerous strongly-lensed features. Following our earlier papers, we combine strong and weak lensing constraints secured with Hubble Space Telescope and Subaru imaging with the radial profile of the stellar velocity dispersion of the central galaxy, essential for separating the baryonic mass distribution in the cluster core. Hydrostatic mass estimates from Chandra X-ray observations further constrain the solution. These combined datasets provide nearly continuous constraints extending from 2 kpc to 1.5 Mpc in radius, allowing stringent tests of results from recent numerical simulations. Two key improvements in our data and its analysis make this the most robust case yet for a shallow slope βof the DM density profile ρ_DM ~ r^-βon small scales. First, following deep Keck spectroscopy, we have secured the stellar velocity dispersion profile to a radius of 26 kpc for the first time in a lensing cluster. Secondly, we improve our previous analysis by adopting a triaxial DM distribution and axisymmetric dynamical models. We demonstate that in this remarkably well-constrained system, the logarithmic slope of the DM density at small radii is β< 1.0 (95% confidence). An improved treatment of baryonic physics is necessary, but possibly insufficient, to reconcile our observations with the recent results of high-resolution simulations.

astro-ph.CO↗

arXiv2010

Asymptotic behavior of the finite-size magnetization as a function of the speed of approach to criticality

The main focus of this paper is to determine whether the thermodynamic magnetization is a physically relevant estimator of the finite-size magnetization. This is done by comparing the asymptotic behaviors of these two quantities along parameter sequences converging to either a second-order point or the tricritical point in the mean-field Blume--Capel model. We show that the thermodynamic magnetization and the finite-size magnetization are asymptotic when the parameter $α$ governing the speed at which the sequence approaches criticality is below a certain threshold $α_0$. However, when $α$ exceeds $α_0$, the thermodynamic magnetization converges to 0 much faster than the finite-size magnetization. The asymptotic behavior of the finite-size magnetization is proved via a moderate deviation principle when $0<α<α_0$ and via a weak-convergence limit when $α>α_0$. To the best of our knowledge, our results are the first rigorous confirmation of the statistical mechanical theory of finite-size scaling for a mean-field model.

math.PR↗

arXiv2010

Early star-forming galaxies and the reionization of the Universe

Star forming galaxies represent a valuable tracer of cosmic history. Recent observational progress with Hubble Space Telescope has led to the discovery and study of the earliest-known galaxies corresponding to a period when the Universe was only ~800 million years old. Intense ultraviolet radiation from these early galaxies probably induced a major event in cosmic history: the reionization of intergalactic hydrogen. New techniques are being developed to understand the properties of these most distant galaxies and determine their influence on the evolution of the universe.

astro-ph.CO↗

arXiv2010

Hubble Space Telescope Studies of Nearby Type Ia Supernovae: The Mean Maximum Light Ultraviolet Spectrum and its Dispersion

We present the first results of an ongoing campaign using the STIS spectrograph on-board the Hubble Space Telescope (HST) whose primary goal is the study of near ultraviolet (UV) spectra of local Type Ia supernovae (SNe Ia). Using events identified by the Palomar Transient Factory and subsequently verified by ground-based spectroscopy, we demonstrate the ability to locate and classify SNe Ia as early as 16 days prior to maximum light. This enables us to trigger HST in a non-disruptive mode to obtain near UV spectra within a few days of maximum light for comparison with earlier equivalent ground-based spectroscopic campaigns conducted at intermediate redshifts, z ~ 0.5. We analyze the spectra of 12 Type Ia supernovae located in the Hubble flow with 0.01 < z < 0.08. Although a fraction of our eventual sample, these data, together with archival data, already provide a substantial advance over that previously available. Restricting samples to those of similar phase and stretch, the mean UV spectrum agrees reasonably closely with that at intermediate redshift, although some differences are found in the metallic absorption features. A larger sample will determine whether these differences reflect possible sample biases or are a genuine evolutionary effect. Significantly, the wavelength-dependent dispersion, which is larger in the UV, follows similar trends to that observed at intermediate redshift and is driven, in part, by differences in the various metallic features. While the origin of the UV dispersion remains uncertain, our comparison suggests that it may reflect compositional variations amongst our sample rather than being predominantly an evolutionary effect.

astro-ph.CO↗

arXiv2010

A coincidence of disturbed morphology and blue UV colour: minor-merger driven star formation in early-type galaxies at z~0.6

We exploit multi-wavelength photometry of early-type galaxies (ETGs) in the COSMOS survey to demonstrate that the low-level star formation activity in the ETG population at intermediate redshift is likely to be driven by minor mergers. Splitting the ETGs into galaxies that show disturbed morphologies indicative of recent merging and those that appear relaxed, we find that ~32% of the ETG population appears to be morphologically disturbed. While the relaxed objects are almost entirely contained within the UV red sequence, their morphologically disturbed counterparts dominate the scatter to blue UV colours, regardless of luminosity. Empirically and theoretically determined major-merger rates in the redshift range z<1 are several times too low to account for the fraction of disturbed ETGs in our sample, suggesting that minor mergers represent the principal mechanism driving the observed star formation activity in our sample. The young stellar components forming in these events have ages between 0.03 and 0.3 Myrs and typically contribute <10% of the stellar mass of the remnant. Together with recent work which demonstrates that the structural evolution of nearby ETGs is consistent with one or more minor mergers, our results indicate that the overall evolution of massive ETGs may be heavily influenced by minor merging at late epochs and highlights the need to systematically study this process in future observational surveys.

astro-ph.CO↗

arXiv2010

Measurement of a Metallicity Gradient in a z=2 Galaxy: Implications for Inside-Out Assembly Histories

We present near-infrared imaging spectroscopy of the strongly-lensed z=2.00 galaxy SDSS J120601.69+514227.8 (`the Clone arc'). Using OSIRIS on the Keck 2 telescope with laser guide star adaptive optics, we achieve resolved spectroscopy with 0.20 arcsecond FWHM resolution in the diagnostic emission lines [O III], Halpha, and [N II]. The lensing magnification allows us to map the velocity and star formation from Halpha emission at a physical resolution of ~300 pc in the galaxy source plane. With an integrated star formation rate of ~50 Msun/yr, the galaxy is typical of sources similarly studied at this epoch. It is dispersion-dominated with a velocity gradient of +/- 80 km/s and average dispersion sigma = 85 km/s; the dynamical mass is 2.4 \times 10^{10} Msun within a half-light radius of 2.9 kpc. Robust detection of [N II] emission across the entire OSIRIS field of view enables us to trace the gas-phase metallicity distribution with 500 pc resolution. We find a strong radial gradient in both the [N II]/Halpha and [O III]/Halpha ratios indicating a metallicity gradient of -0.27 +/- 0.05 dex/kpc with central metallicity close to solar. We demonstrate that the gradient is seen independently in two multiple images. While the physical gradient is considerably steeper than that observed in local galaxies, in terms of the effective radius at that epoch, the gradient is similar. This suggests that subsequent growth occurs in an inside-out manner with the inner metallicity gradient diminished over time due to radial mixing and enrichment from star formation.

astro-ph.CO↗

arXiv2010

Keck Spectroscopy of Faint 3<z<7 Lyman Break Galaxies:- II. A High Fraction of Line Emitters at Redshift Six

As Lyman-alpha photons are scattered by neutral hydrogen, a change with redshift in the Lyman-alpha equivalent width distribution of distant galaxies offers a promising probe of the degree of ionization in the intergalactic medium and hence when cosmic reionization ended. This simple test is complicated by the fact that Lyman-alpha emission can also be affected by the evolving astrophysical details of the host galaxies. In the first paper in this series, we demonstrated both a luminosity and redshift dependent trend in the fraction of Lyman-alpha emitters seen within color-selected Lyman-break galaxies (LBGs) over the range 3 25 A) emission, an increase of 1.6x from a similar sample observed at z~4. With a total sample of 74 z~6 LBGs, we determine the luminosity-dependent Lyman-alpha equivalent width distribution. Assuming continuity in these trends to the new population of z~7 sources located with the Hubble WFC3/IR camera, we predict that unless the neutral fraction rises in the intervening 200 Myr, the success rate for spectroscopic confirmation using Lyman-alpha emission should be high.

astro-ph.CO↗

arXiv2010

The Type Ia Supernova Rate in Redshift 0.5--0.9 Galaxy Clusters

Supernova (SN) rates are potentially powerful diagnostics of metal enrichment and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials and relatively simple star-formation histories. We have carried out a survey for supernovae (SNe) in galaxy clusters, at a redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We reimaged a sample of 15 clusters that were previously imaged by ACS, thus obtaining two to three epochs per cluster, in which we discovered five likely cluster SNe, six possible cluster SNe Ia, two hostless SN candidates, and several background and foreground events. Keck spectra of the host galaxies were obtained to establish cluster membership. We conducted detailed efficiency simulations, and measured the stellar luminosities of the clusters using Subaru images. We derive a cluster SN rate of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01 (systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM +0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic) [where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of cluster SN rates, the uncertainties are dominated by small-number statistics. The SN rate in this redshift bin is consistent with the SN rate in clusters at lower redshifts (to within the uncertainties), and shows that there is, at most, only a slight increase of cluster SN rate with increasing redshift. The low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron mass in clusters was already in place by z~1. The recently observed doubling of iron abundances in the intracluster medium between z=1 and 0, if real, is likely the result of redistribution of existing iron, rather than new production of iron.

astro-ph.CO↗

arXiv2010

Keck Spectroscopy of z>1 Field Spheroidals: Dynamical Constraints on the Growth Rate of Red "Nuggets"

We present deep Keck spectroscopy for 17 morphologically-selected field spheroidals in the redshift range 1.05 10^11 Msol) grew in size over 0 Mdyn > 10^10 Msol) did not grow significantly. These trends are consistent with a picture in which more massive spheroidals formed at higher redshift via "wetter" mergers involving greater dissipation. To examine growth under the favored "dry" merger hypothesis, we also examine size growth at a fixed velocity dispersion. This test, uniquely possible with our dynamical data, allows us to consider the effects of "progenitor bias." Above our completeness limit (sigma > 200 km/s), we find size growth consistent with that inferred for the mass-selected sample, thus ruling out strong progenitor bias. To maintain continuity in the growth of massive galaxies over the past 10 Gyr, our new results imply that size evolution over 1.3 2 are truly massive and compact.

astro-ph.CO↗

arXiv2010

Keck Spectroscopy of Faint 3<z<7 Lyman Break Galaxies: - I. New constraints on cosmic reionisation from the luminosity and redshift-dependent fraction of Lyman-alpha emission

We present results from a new Keck spectroscopic survey of UV-faint LBGs in the redshift range 3<z<7. Combined with earlier Keck and published ESO VLT data, our sample contains more than 600 dropouts, offering new insight into the nature of sub-L* sources typical of those likely to dominate the cosmic reionisation process. Here we use this sample to characterise the fraction of strong Lya emitters within the continuum-selected dropouts. By quantifying how the "Lya fraction" varies with redshift, we seek to constrain changes in Lya transmission associated with reionisation. In order to distinguish the effects of reionisation from other factors which affect the Lya fraction (e.g. dust, ISM kinematics), we study the luminosity and redshift-dependence of the Lya fraction over 3<z<6, when the IGM is known to be ionised. These results reveal that low luminosity galaxies show strong Lya emission much more frequently than luminous systems, and that at fixed luminosity, the prevalence of strong Lya emission increases moderately with redshift over 3 < z < 6. Based on the correlation between blue UV slopes and strong Lya emitting galaxies in our dataset, we argue that the Lya fraction trends are governed by redshift and luminosity-dependent variations in the dust obscuration, with likely additional contributions from trends in the kinematics and covering fraction of neutral hydrogen. We find a tentative decrease in the Lya fraction at z~7 based on the limited IR spectra for candidate z~7 lensed LBGs, a result which, if confirmed with future surveys, would suggest an increase in the neutral fraction by this epoch. Given the supply of z and Y-drops now available from Hubble WFC3/IR surveys, we show it will soon be possible to significantly improve estimates of the Lya fraction using optical and near-IR spectrographs, thereby extending the study conducted in this paper to 7<z<8.

astro-ph.CO↗

arXiv2009

Environmental Effects in the Evolution of Galactic Bulges

We investigate possible environmental trends in the evolution of galactic bulges over the redshift range 0 =0.4 and =0.54 using surface photometry based on HST imaging and velocity dispersions based on Keck spectroscopy. As a reference point for our study we include data for pure ellipticals, which we model as single-component Sersic profiles; whereas for multi-component galaxies we undertake decompositions using Sersic and exponential models for the bulge and disk respectively. Although the FP for both distant cluster and field samples are offset from the local relation, consistent with evolutionary trends found in earlier studies, we detect significant differences in the zero point of ~=0.2 dex between the field and cluster samples at a given redshift. For both clusters, the environmentally-dependent offset is in the sense expected for an accelerated evolution of bulges in dense environments. By matching the mass range of our samples, we confirm that this difference does not arise as a result of the mass-dependent downsizing effects seen in larger field samples. Our result is also consistent with the hypothesis that - at fixed mass and environment - the star formation histories of galactic bulges and pure spheroids are indistinguishable, and difficult to reconcile with the picture whereby the majority of large bulges form primarily via secular processes within spiral galaxies.

astro-ph.CO↗

arXiv2009

Probing $\sim L_{*}$ Lyman-break Galaxies at $z\approx 7$ in GOODS-South with WFC3 on HST

We analyse recently acquired near-infrared Hubble Space Telescope imaging of the GOODS-South field to search for star forming galaxies at z~7.0. By comparing WFC 3 0.98 micron Y-band images with ACS z-band (0.85 micron) images, we identify objects with colours consistent with Lyman break galaxies at z~6.4-7.4. This new data covers an area five times larger than that previously reported in the WFC3 imaging of the Hubble Ultra Deep Field, and affords a valuable constraint on the bright end of the luminosity function. Using additional imaging of the region in the ACS B, V and i-bands from GOODS v2.0 and the WFC3 J-band we attempt to remove any low-redshift interlopers. Our selection criteria yields 6 candidates brighter than Y_AB = 27.0, of which all except one are detected in the ACS z-band imaging and are thus unlikely to be transients. Assuming all 6 candidates are at z~7 this implies a surface density of objects brighter than Y_AB = 27.0 of 0.30\pm0.12 arcmin-2, a value significantly smaller than the prediction from the z ~ 6 luminosity function. This suggests continued evolution of the bright end of the luminosity function between z = 6 to 7, with number densities lower at higher redshift.

astro-ph.CO↗

arXiv2009

Comet C/2004 Q2 (MACHHOLZ): Parent Volatiles, a Search for Deuterated Methane, and Constraint on the CH4 Spin Temperature

High-dispersion (l/dl ~ 25,000) infrared spectra of Comet C/2004 Q2 (Machholz) were acquired on Nov. 28-29, 2004, and Jan. 19, 2005 (UT dates) with NIRSPEC at the Keck-2 telescope on Mauna Kea. We detected H2O, CH4, C2H2, C2H6, CO, H2CO, CH3OH, HCN, and NH3 and we conducted a sensitive search for CH3D. We report rotational temperatures, production rates, and mixing ratios (with respect to H2O) at heliocentric distances of 1.49 AU (Nov. 2004) and 1.21 AU (Jan. 2005). We highlight three principal results: (1) The mixing ratios of parent volatiles measured at 1.49 AU and 1.21 AU agree within confidence limits, consistent with homogeneous composition in the mean volatile release from the nucleus of C/2004 Q2. Notably, the relative abundance of C2H6/C2H2 is substantially higher than those measured in other comets, while the mixing ratios C2H6/H2O, CH3OH/H2O, and HCN/H2O are similar to those observed in comets, referred to as "organics-normal". (2) The spin temperature of CH4 is > 35-38 K, an estimate consistent with the more robust spin temperature found for H2O. (3) We obtained a 3s upper limit of CH3D/CH4 < 0.020 (D/H < 0.005). This limit suggests that methane released from the nucleus of C/2004 Q2 is not dominated by a component formed in extremely cold (near 10 K) environments. Formation pathways of both interstellar and nebular origin consistent with the measured D/H in methane are discussed. Evaluating the relative contributions of these pathways requires further modeling of chemistry including both gas-phase and gas-grain processes in the natal interstellar cloud and in the protoplanetary disk.

astro-ph.EP↗

arXiv2009

Detection of PAH and Far-Infrared Emission from the Cosmic Eye: Probing the Dust and Star Formation of Lyman Break Galaxies

We report the results of a Spitzer infrared study of the Cosmic Eye, a strongly lensed, L*_UV Lyman Break Galaxy (LBG) at z=3.074. We obtained Spitzer IRS spectroscopy as well as MIPS 24 and 70 micron photometry. The Eye is detected with high significance at both 24 and 70 microns and, when including a flux limit at 3.5 mm, we estimate an infrared luminosity of L_IR = 8.3 (+4.7-4.4) x10^11 L_sun assuming a magnification of 28+-3. This L_IR is eight times lower than that predicted from the rest-frame UV properties assuming a Calzetti reddening law. This has also been observed in other young LBGs, and indicates that the dust reddening law may be steeper in these galaxies. The mid-IR spectrum shows strong PAH emission at 6.2 and 7.7 microns, with equivalent widths near the maximum values observed in star-forming galaxies at any redshift. The L_PAH-to-L_IR ratio lies close to the relation measured in local starbursts. Therefore, L_PAH or L_MIR may be used to estimate L_IR and thus, star formation rate, of LBGs, whose fluxes at longer wavelengths are typically below current confusion limits. We also report the highest redshift detection of the 3.3 micron PAH emission feature. The PAH ratio, L_6.2/L_3.3=5.1+- 2.7, and the PAH-to-L_IR ratio, L_3.3/L_IR = 8.5 +- 4.7 x10^-4, are both in agreement with measurements in local starbursts and ULIRGs, suggesting that this line may serve as a good proxy for L_PAH or L_IR at z > 3 with the James Webb Space Telescope.

astro-ph.CO↗