arXiv subjects

Scott Chapman

Publications and source records attributed to Scott Chapman.

At least 127 records · Page 7Linked to original sources

arXiv2011

PAndAS' progeny: extending the M31 dwarf galaxy cabal

We present the discovery of five new dwarf galaxies, Andromeda XXIII-XXVII, located in the outer halo of M31. These galaxies were found in the second year of data from the Pan-Andromeda Archaeological Survey (PAndAS) of the M31/M33 subgroup. This survey now provides an almost complete panoramic view of the M31 halo out to an average projected radius of ~150 kpc. The metal-poor stellar density map for this whole region serves, not only as an illustration of the discovery space for satellite galaxies, but also gives a birds-eye view of the ongoing assembly process of an L* disk galaxy. Four of the new dwarfs appear as well-defined spatial over-densities of stars lying on the expected locus of metal-poor red giant branch stars at the distance of M31. The fifth over-density, And XXVII, is embedded in an extensive stream of such stars and is possibly the remnant of a strong tidal disruption event. All five satellites have metallicities and luminosities typical of dwarf spheroidal galaxies and continue the trend whereby the brighter dwarf spheroidal satellites of M31 generally have much larger half-light radii than their Milky Way counterparts. With an extended sample of M31 satellite galaxies we also revisit the spatial distribution of this population and find that, within the current limits of the PAndAS survey, the surface density of satellites is essentially constant out to 150 kpc. This corresponds to a radial density distribution of satellites varying as 1/r, a result seemingly in conflict with the predictions of cosmological simulations. (Abridged)

astro-ph.CO↗

arXiv2010

Detection of molecular gas in a distant submillimetre galaxy at z=4.76 with ATCA

We have detected the CO(2-1) transition from the submillimetre galaxy (SMG) LESSJ033229.4-275619 at z=4.755 using the new Compact Array Broadband Backend system on the Australian Telescope Compact Array. These data have identified a massive gas reservoir available for star formation for the first time in an SMG at z~5. We use the luminosity and velocity width (FWHM of 160 km/s) of the CO(2--1) line emission to constrain the gas and dynamical mass of Mgas~1.6x10^10 Msun and Mdyn(<2kpc)~5x10^10 (0.25/sin^2(i)) Msun, respectively, similar to that observed for SMGs at lower redshifts of z~2-4, although we note that our observed CO FWHM is a factor of ~3 narrower than typically seen in SMGs. Together with the stellar mass we estimate a total baryonic mass of Mbary~1x10^11 Msun, consistent with the dynamical mass for this young galaxy within the uncertainties. Dynamical and baryonic mass limits of high-redshift galaxies are useful tests of galaxy formation models: using the known z~4-5 SMGs as examples of massive baryonic systems, we find that their space density is consistent with that predicted by current galaxy formation models. In addition, these observations have helped to confirm that z~4-5 SMGs possess the baryonic masses and gas consumption timescales necessary to be the progenitors of the luminous old red galaxies seen at z~3. Our results provide a preview of the science that ALMA will enable on the formation and evolution of the earliest massive galaxies in the Universe.

astro-ph.CO↗

arXiv2010

The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a shallow and wide submillimeter imaging survey with SPIRE

A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere (3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which have extensive multi-wavelength coverage and are easily accessible from ALMA. Two thirds of the of the sources are expected to be at z > 1, one third at z > 2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary anisotropy studies with Planck and ground-based CMB data. (c) Find at least 1200 strongly lensed bright sub-mm sources leading to a 2% test of general relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an unbiased study of the environmental dependence of star formation. (e) Perform an unbiased survey for star formation and dust at high Galactic latitude and make a census of debris disks and dust around AGB stars and white dwarfs.

astro-ph.CO↗

arXiv2010

Evidence for an accretion origin for the outer halo globular cluster system of M31

We use a sample of newly-discovered globular clusters from the Pan-Andromeda Archaeological Survey (PAndAS) in combination with previously-catalogued objects to map the spatial distribution of globular clusters in the M31 halo. At projected radii beyond ~30 kpc, where large coherent stellar streams are readily distinguished in the field, there is a striking correlation between these features and the positions of the globular clusters. Adopting a simple Monte Carlo approach, we test the significance of this association by computing the probability that it could be due to the chance alignment of globular clusters smoothly distributed in the M31 halo. We find the likelihood of this possibility is low, below 1%, and conclude that the observed spatial coincidence between globular clusters and multiple tidal debris streams in the outer halo of M31 reflects a genuine physical association. Our results imply that the majority of the remote globular cluster system of M31 has been assembled as a consequence of the accretion of cluster-bearing satellite galaxies. This constitutes the most direct evidence to date that the outer halo globular cluster populations in some galaxies are largely accreted.

astro-ph.GA↗

arXiv2010

A Hubble Space Telescope NICMOS and ACS Morphological Study of z~2 Submillimetre Galaxies

We present a quantitative morphological analysis using HST NICMOS H160- and ACS I775- band imaging of 25 spectroscopically confirmed submillimetre galaxies (SMGs) which have redshifts between z=0.7-3.4. Our analysis also employs a comparison sample of more typical star-forming galaxies at similar redshifts (such as LBGs) which have lower far-infrared luminosities. This is the first large-scale study of the morphologies of SMGs in the near-infrared at ~0.1" resolution (<1kpc). We find that the half light radii of the SMGs (r_h=2.3+/-0.3 and 2.8+/-0.4kpc in the observed I- and H-bands respectively) and asymmetries are not statistically distinct from the comparison sample of star-forming galaxies. However, we demonstrate that the SMG morphologies differ more between the rest-frame UV and optical-bands than typical star-forming galaxies and interpret this as evidence for structured dust obscuration. We show that the composite observed H-band light profile of SMGs is better fit with a Sersic index with n~2, suggesting the stellar structure of SMGs is best described by a spheroid/elliptical galaxy light distribution. We also compare the sizes and stellar masses of SMGs to local and high-redshift populations, and find that the SMGs have stellar densities which are comparable to local early-type galaxies, as well as luminous, red and dense galaxies at z~1.5 which have been proposed as direct SMG descendants, although the SMG stellar masses and sizes are systematically larger. Overall, our results suggest that the physical processes occuring within the galaxies are too complex to be simply characterised by the rest-frame UV/optical morphologies which appear to be essentially decoupled from all other observables, such as bolometric luminosity, stellar or dynamical mass.

astro-ph.CO↗

arXiv2009

PT-Invariance and Indefinite Metric

A new proof is given for why the non-Hermitian, PT-Invariant cubic oscillator with imaginary coupling has real eigenvalues. The proof consists of two steps. In the first step, it is shown that for many PT-Invariant Hamiltonians, one can define corresponding Hermitian Hamiltonians that have the same eigenvalues when quantized using indefinite metric. The second step is to show that the indefinite-metric eigenvalues of the Hermitian cubic oscillator are real since the norms of its eigenstates do not vanish. The correspondence between PT-Invariant Hamiltonians and indefinite-metric Hermitian Hamiltonians is further discussed as a way to determine vacuum stability for certain supersymmetric gauge theories.

math-ph↗

arXiv2009

PAndAS' cubs: discovery of two new dwarf galaxies in the surroundings of the Andromeda and Triangulum galaxies

We present the discovery of two new dwarf galaxies, Andromeda XXI and Andromeda XXII, located in the surroundings of the Andromeda and Triangulum galaxies (M31 and M33). These discoveries stem from the first year data of the Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the M31/M33 group conducted with the Megaprime/MegaCam wide-field camera mounted on the Canada-France-Hawaii Telescope. Both satellites appear as spatial overdensities of stars which, when plotted in a color-magnitude diagram, follow metal-poor, [Fe/H]=-1.8, red giant branches at the distance of M31/M33. Andromeda XXI is a moderately bright dwarf galaxy (M_V=-9.9+/-0.6), albeit with low surface brightness, emphasizing again that many relatively luminous M31 satellites still remain to be discovered. It is also a large satellite, with a half-light radius close to 1 kpc, making it the fourth largest Local Group dwarf spheroidal galaxy after the recently discovered Andromeda XIX, Andromeda II and Sagittarius around the Milky Way, and supports the trend that M31 satellites are larger than their Milky Way counterparts. Andromeda XXII is much fainter (M_V=-6.5+/-0.8) and lies a lot closer in projection to M33 than it does to M31 (42 vs. 224 kpc), suggesting that it could be the first Triangulum satellite to be discovered. Although this is a very exciting possibility in the context of a past interaction of M33 with M31 and the fate of its satellite system, a confirmation will have to await a good distance estimate to confirm its physical proximity to M33. Along with the dwarf galaxies found in previous surveys of the M31 surroundings, these two new satellites bring the number of dwarf spheroidal galaxies in this region to 20.

astro-ph.CO↗

arXiv2009

The disappearance of Lyman alpha blobs: a GALEX search at z=0.8

Lyman alpha blobs - luminous, spatially extended emission-line nebulae, often lacking bright continuum counterparts - are common in dense environments at high redshift. Until recently, atmospheric absorption and filter technology have limited our knowledge of any similar objects at z<2. We use GALEX slitless spectroscopy to search for similar objects in the rich environments of two known cluster and supercluster fields at z=0.8, where the instrumental sensitivity peaks. The regions around Cl 1054-0321 and Cl 0023+0423 were each observed in slitless-spectrum mode for 10-19 ksec, with accompanying direct images of 3-6 ksec to assist in recognizing continuum sources. Using several detection techniques, we find no resolved Lyman alpha emitters to a flux limit of(1.5-9) x 10^{-15} erg/ cm^2 s, on size scales of 5-30 arcseconds. This corresponds to line luminosities of (0.5-3) x 10^43 erg/s for linear scales 35-200 kpc. Comparison with both blind and targeted surveys at higher redshifts indicates that the population must have evolved in comoving density at least as strongly as (1+z)^3. These results suggest that the population of Lyman alpha blobs is specific to the the high-redshift Universe.

astro-ph.GA↗

arXiv2009

A submillimetre galaxy at z=4.76 in the LABOCA survey of the Extended Chandra Deep Field South

We report on the identification of the highest redshift submm-selected source currently known: LESSJ033229.4-275619. This source was detected in the Large Apex BOlometer CAmera (LABOCA) Extended Chandra Deep Field South (ECDFS) Submillimetre Survey (LESS), a sensitive 870-um survey (~1.2-mJy rms) of the full 30'x30' ECDFS with the LABOCA camera on the Atacama Pathfinder EXperiment (APEX) telescope. The submm emission is identified with a radio counterpart for which optical spectroscopy provides a redshift of z=4.76. We show that the bolometric emission is dominated by a starburst with a star formation rate of ~1000 Msun/yr, although we also identify a moderate luminosity Active Galactic Nucleus (AGN) in this galaxy. Thus it has characteristics similar to those of z~2 submm galaxies (SMGs), with a mix of starburst and obscured AGN signatures. This demonstrates that ultraluminous starburst activity is not just restricted to the hosts of the most luminous (and hence rare) QSOs at z~5, but was also occurring in less extreme galaxies at a time when the Universe was less than 10% of its current age. Assuming that we are seeing the major phase of star formation in this galaxy, then we demonstrate that it would be identified as a luminous distant red galaxy at z~3 and that the current estimate of the space density of z>4 SMGs is only sufficient to produce ~10% of the luminous red galaxy population at these early times. However, this leaves open the possibility that some of these galaxies formed through less intense, but more extended star formation events. If the progenitors of all of the luminous red galaxies at z~3 go through an ultraluminous starburst at z>4 then the required volume density of z>4 SMGs will exceed that predicted by current galaxy formation models by more than an order of magnitude.

astro-ph.GA↗

arXiv2008

Mass Generation from Higgs-like Ghosts

Covariant quantization of gauge theories generally requires the inclusion of Fadeev Popov ghosts in the gauge-fixed Lagrangian. Normally these ghosts have fermionic statistics, but in supersymmetric theories that include fermionic gauge fields, there can also be ghosts with bosonic statistics. Since these ghosts are scalar bosons, they can have vacuum expectation values (VEVs) without violating Lorentz invariance. In particular, for the supersymmetric group SU(2/3), one can choose a gauge with a Higgs-like bosonic ghost potential that is minimized when one of the ghosts develops a VEV. This VEV breaks the SU(2) x U(1) subgroup of SU(2/3) down to U(1) and spontaneously generates vector boson masses, but without the "hierarchy" problems that accompany the Higgs field. SU(2/3) also has an SU(3) subgroup, and unitarity requires that the SU(3) gauge bosons must be confined. Since bosonic ghosts do not exist as particles asymptotically, this kind of theory could be a possible explanation if no Higgs Boson is detected at the LHC.

hep-ph↗

arXiv2008

The Properties of Sub-mm Galaxies in Hierarchical Models

We use the combined GALFORM semi-analytical model of galaxy formation and GRASIL spectrophotometric code to investigate the properties of galaxies selected via their sub-mm emission. Our fiducial model has previously been shown to fit the properties of local ULIRGs, as well as the number counts of faint sub-mm galaxies. Here, we test the model in detail by comparing the SEDs and stellar, dynamical, gas and halo masses of sub-mm galaxies against observational data. We precisely mimic the sub-mm and radio selection function of the observations and show that the predicted far-infrared properties of model galaxies with S_850>5mJy and S_1.4>30uJy are in good agreement with observations. Although the dust emission model does not assume a single dust temperature, the far-infrared SEDs are well described by single component modified black-body spectrum with characteristic temperature 32+/-5K. We also find evidence that the observations may have uncovered evolution in the far-infrared--radio relation in ULIRGs out to z~2. We show that the predicted redshift distribution of sub-mm galaxies provides a reasonable fit to the observational data with a median redshift z=2.0, with the radio-selected subset predicted to make up approximately 75% of the population. However, the predicted K-band and mid-infrared (3--8um) flux densities of the sub-mm galaxies (and LBGs) are up to a factor 10x fainter than observed. This discrepancy may indicate that the stellar masses of the sub-mm galaxies in the model are too low: M~10^10Mo, while observations suggest more massive systems, M~10^11Mo. Finally, we discuss the potential modifications to the models which may improve the fit to the observational data. [Abridged]

astro-ph↗

arXiv2008

A trio of new Local Group galaxies with extreme properties

We report on the discovery of three new dwarf galaxies in the Local Group. These galaxies are found in new CFHT/MegaPrime g,i imaging of the south-western quadrant of M31, extending our extant survey area to include the majority of the southern hemisphere of M31's halo out to 150 kpc. All these galaxies have stellar populations which appear typical of dwarf spheroidal (dSph) systems. The first of these galaxies, Andromeda XVIII, is the most distant Local Group dwarf discovered in recent years, at ~1.4 Mpc from the Milky Way (~ 600 kpc from M31). The second galaxy, Andromeda XIX, a satellite of M31, is the most extended dwarf galaxy known in the Local Group, with a half-light radius of r_h ~ 1.7 kpc. This is approximately an order of magnitude larger than the typical half-light radius of many Milky Way dSphs, and reinforces the difference in scale sizes seen between the Milky Way and M31 dSphs (such that the M31 dwarfs are generally more extended than their Milky Way counterparts). The third galaxy, Andromeda XX, is one of the faintest galaxies so far discovered in the vicinity of M31, with an absolute magnitude of order M_V ~ -6.3. Andromeda XVIII, XIX and XX highlight different aspects of, and raise important questions regarding, the formation and evolution of galaxies at the extreme faint-end of the luminosity function. These findings indicate that we have not yet sampled the full parameter space occupied by dwarf galaxies, although this is an essential pre-requisite for successfully and consistently linking these systems to the predicted cosmological dark matter sub-structure.

astro-ph↗

arXiv2007

The SCUBA HAlf Degree Extragalactic Survey (SHADES) -- VI. 350 micron mapping of submillimetre galaxies

A follow-up survey using the Submillimetre High-Angular Resolution Camera (SHARC-II) at 350 microns has been carried out to map the regions around several 850 micron-selected sources from the Submillimetre HAlf Degree Extragalactic Survey (SHADES). These observations probe the infrared luminosities and hence star-formation rates in the largest existing, most robust sample of submillimetre galaxies (SMGs). We measure 350 micron flux densities for 24 850 micron sources, seven of which are detected at >2.5-sigma within a 10 arcsec search radius of the 850 micron positions. When results from the literature are included the total number of 350 micron flux density constraints of SHADES SMGs is 31, with 15 detections. We fit a modified blackbody to the far-infrared (FIR) photometry of each SMG, and confirm that typical SMGs are dust-rich (Mdust~9x10^8 Msun), luminous (Lfir~2x10^12 Lsun), star-forming galaxies with intrinsic dust temperatures of ~35 K and star-formation rates of ~400 Msun/yr. We have measured the temperature distribution of SMGs and find that the underlying distribution is slightly broader than implied by the error bars, and that most SMGs are at 28 K with a few hotter. We also place new constraints on the 350 micron source counts, N350(>25mJy)~200-500 deg^-2.

astro-ph↗

arXiv2007

SU(3) Ghosts with Spin

A new Lorentz-covariant gauge is presented for SU(3). In this gauge, both the ghosts and the gauge fields in the (4, 5, 6, 7) gauge directions acquire half-integral spin. As a result, the ghosts in these directions have the correct relationship between spin and statistics, while the gauge fields have the incorrect relationship. Consequently, asymptotic ghost states are not forbidden in this gauge and can possibly form new matter states. Conversely, asymptotic gauge fields in the (4, 5, 6, 7) directions are forbidden in this gauge, so the SU(3) symmetry is broken down to an SU(2)xU(1) symmetry asymptotically.

hep-th↗

arXiv2007

The SCUBA HAlf Degree Extragalactic Survey (SHADES) - IV: Radio-mm-FIR photometric redshifts

We present the redshift distribution of the SHADES galaxy population based on the rest-frame radio-mm-FIR colours of 120 robustly detected 850um sources in the Lockman Hole East (LH) and Subaru XMM-Newton Deep Field (SXDF). The redshift distribution derived from the full SED information is shown to be narrower than that determined from the radio-submm spectral index, as more photometric bands contribute to a higher redshift accuracy. The redshift distribution of sources derived from at least two photometric bands peaks at z ~ 2.4 and has a near-Gaussian distribution, with 50 per cent (interquartile range) of sources at z=1.8-3.1. We find a statistically-significant difference between the measured redshift distributions in the two fields; the SXDF peaking at a slightly lower redshift (median z ~ 2.2) than the LH (median z ~ 2.7), which we attribute to the noise-properties of the radio observations. We demonstrate however that there could also be field-to-field variations that are consistent with the measured differences in the redshift distributions, and hence, that the incomplete area observed by SHADES with SCUBA, despite being the largest sub-mm survey to date, may still be too small to fully characterize the bright sub-mm galaxy population. Finally we present a brief comparison with the predicted, or assumed, redshift distributions of sub-mm galaxy formation and evolution models, and we derive the contribution of these SHADES sources and the general sub-mm galaxy population to the star formation-rate density at different epochs.

astro-ph↗

arXiv2007

Symmetry Breaking in BRST Quantization of SU(3)

New BRST-invariant states for SU(3) gauge field theory are presented. The states have finite norms and unlike the states that are usually used to derive path integrals, they break SU(3) symmetry by choosing preferred gauge directions. This symmetry breaking may also give effective masses to some of the gauge bosons of the theory.

hep-th↗

arXiv2006

New Ghost States in SU(3) Gauge Field Theory

The ghost sector of SU(3) gauge field theory is studied, and new BRST-invariant states are presented that do not have any analog in other SU(N) field theories. The new states come in either ghost doublets or triplets, and they appear exclusively in SU(3) due to the fact that the non-Abelian part of the BRST charge has 3 ghost operators, while SU(3) has 3 pairs of off-diagonal gauge constraints. The states have finite, positive norms even though the triplet states do not have well-defined ghost numbers. It is speculated that this special nature of the ghost sector of SU(3) could play some role in QCD confinement.

hep-th↗

arXiv2006

Draco, a flawless dwarf galaxy

The Draco dwarf spheroidal galaxy (dSph), with its apparent immense mass to light ratio and compact size, holds many clues to the nature of the enigmatic dark matter. Here we present deep photometric studies of this dwarf galaxy, undertaken with the MegaCam Camera at the Canada-France-hawaii Telescope, the Wide Field Camera at the Isaac Newton Telescope and the Wide-Field and Planetary Camera on board the Hubble Space Telescope. The new photometric data cover the entirety of the galaxy, and reach i=24.5 at 50% completeness, significantly deeper than previous panoramic studies, allowing searches for tidal disturbances of much lower surface brightness than has been possible before. With these improved statistics, we find no evidence for asymmetric disturbances or tidal tails that possess more than 3% of the stars found within the centre of the galaxy. We find that the central stellar density, as probed by the HST data, rises into the central 0.5'. Uncertainties in the position of the centroid of the galaxy do not allow us to determine whether the apparent flattening of the profile interior to 0.5' is reliable or not. Draco is therefore a flawless dwarf galaxy, featureless and apparently unaffected by Galactic tides.

astro-ph↗