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S. Dye

Publications and source records attributed to S. Dye.

At least 91 records · Page 5Linked to original sources

Herschel-ATLAS/GAMA: a census of dust in optically selected galaxies from stacking at submillimetre wavelengths

We use the Herschel-ATLAS survey to conduct the first large-scale statistical study of the submm properties of optically selected galaxies. Using ~80,000 r-band selected galaxies from 126 deg^2 of the GAMA survey, we stack into submm imaging at 250, 350 and 500μm to gain unprecedented statistics on the dust emission from galaxies at z < 0.35. We find that low redshift galaxies account for 5% of the cosmic 250μm background (4% at 350μm; 3% at 500μm), of which approximately 60% comes from 'blue' and 20% from 'red' galaxies (rest-frame g - r). We compare the dust properties of different galaxy populations by dividing the sample into bins of optical luminosity, stellar mass, colour and redshift. In blue galaxies we find that dust temperature and luminosity correlate strongly with stellar mass at a fixed redshift, but red galaxies do not follow these correlations and overall have lower luminosities and temperatures. We make reasonable assumptions to account for the contaminating flux from lensing by red sequence galaxies and conclude that galaxies with different optical colours have fundamentally different dust emission properties. Results indicate that while blue galaxies are more luminous than red galaxies due to higher temperatures, the dust masses of the two samples are relatively similar. Dust mass is shown to correlate with stellar mass, although the dust/stellar mass ratio is much higher for low stellar mass galaxies, consistent with the lowest mass galaxies having the highest specific star formation rates. We stack the 250μm/NUV luminosity ratio, finding results consistent with greater obscuration of star formation at lower stellar mass and higher redshift. Submm luminosities and dust masses of all galaxies are shown to evolve strongly with redshift, indicating a fall in the amount of obscured star formation in ordinary galaxies over the last four billion years.

astro-ph.CO↗

Herschel-ATLAS: towards a sample of ~1000 strongly-lensed galaxies

While the selection of strongly lensed galaxies with 500μm flux density S_500>100 mJy has proven to be rather straightforward (Negrello et al. 2010), for many applications it is important to analyze samples larger than the ones obtained when confining ourselves to such a bright limit. Moreover, only by probing to fainter flux densities is possible to exploit strong lensing to investigate the bulk of the high-z star-forming galaxy population. We describe HALOS (the Herschel-ATLAS Lensed Objects Selection), a method for efficiently selecting fainter candidate strongly lensed galaxies, reaching a surface density of ~1.5-2 deg^-2, i.e. a factor of about 4 to 6 higher than that at the 100 mJy flux limit. HALOS will allow the selection of up to ~1000 candidate strongly lensed galaxies (with amplifications μ>2) over the full H-ATLAS survey area. Applying HALOS to the H-ATLAS Science Demonstration Phase field (~14.4 deg^2) we find 31 candidate strongly lensed galaxies, whose candidate lenses are identified in the VIKING near-infrared catalog. Using the available information on candidate sources and candidate lenses we tentatively estimate a ~72% purity of the sample. The redshift distribution of the candidate lensed sources is close to that reported for most previous surveys for lensed galaxies, while that of candidate lenses extends to substantially higher redshifts than found in the other surveys. The counts of candidate strongly lensed galaxies are also in good agreement with model predictions (Lapi et al. 2011). Even though a key ingredient of the method is the deep near-infrared VIKING photometry, we show that H-ATLAS data alone allow the selection of a similarly deep sample of candidate strongly lensed galaxies with an efficiency close to 50%; a slightly lower surface density (~1.45 deg^-2) can be reached with a ~70% efficiency.

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The 2010 Interim Report of the Long-Baseline Neutrino Experiment Collaboration Physics Working Groups

In early 2010, the Long-Baseline Neutrino Experiment (LBNE) science collaboration initiated a study to investigate the physics potential of the experiment with a broad set of different beam, near- and far-detector configurations. Nine initial topics were identified as scientific areas that motivate construction of a long-baseline neutrino experiment with a very large far detector. We summarize the scientific justification for each topic and the estimated performance for a set of far detector reference configurations. We report also on a study of optimized beam parameters and the physics capability of proposed Near Detector configurations. This document was presented to the collaboration in fall 2010 and updated with minor modifications in early 2011.

hep-ex↗

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses IX. Time delays, lens dynamics and baryonic fraction in HE 0435-1223

We present accurate time delays for the quadruply imaged quasar HE 0435-1223. The delays were measured from 575 independent photometric points obtained in the R-band between January 2004 and March 2010. With seven years of data, we clearly show that quasar image A is affected by strong microlensing variations and that the time delays are best expressed relative to quasar image B. We measured Delta_t(BC) = 7.8+/-0.8 days, Delta_t(BD) = -6.5+/-0.7 days and Delta_t_CD = -14.3+/-0.8 days. We spacially deconvolved HST NICMOS2 F160W images to derive accurate astrometry of the quasar images and to infer the light profile of the lensing galaxy. We combined these images with a stellar population fitting of a deep VLT spectrum of the lensing galaxy to estimate the baryonic fraction, $f_b$, in the Einstein radius. We measured f_b = 0.65+0.13-0.10 if the lensing galaxy has a Salpeter IMF and f_b = 0.45+0.04-0.07 if it has a Kroupa IMF. The spectrum also allowed us to estimate the velocity dispersion of the lensing galaxy, sigma_ap = 222+/-34 km/s. We used f_b and sigma_ap to constrain an analytical model of the lensing galaxy composed of an Hernquist plus generalized NFW profile. We solve the Jeans equations numerically for the model and explored the parameter space under the additional requirement that the model must predict the correct astrometry for the quasar images. Given the current error bars on f_b and sigma_ap, we did not constrain H0 yet with high accuracy, i.e., we found a broad range of models with chi^2 < 1. However, narrowing this range is possible, provided a better velocity dispersion measurement becomes available. In addition, increasing the depth of the current HST imaging data of HE 0435-1223 will allow us to combine our constraints with lens reconstruction techniques that make use of the full Einstein ring that is visible in this object.

astro-ph.CO↗

H-ATLAS/GAMA: Dusty early-type galaxies and passive spirals

We present the dust properties and star-formation histories of local submillimetre-selected galaxies in Herschel-ATLAS, classified by optical morphology. The early-type galaxies (ETGs) that are detected contain as much dust as typical spirals, and form a unique sample that has been blindly selected at submillimetre wavelengths. Comparing H-ATLAS galaxies to a control sample of optically selected galaxies, we find 5.5% of luminous ETGs are detected in H-ATLAS. The H-ATLAS ETGs contain a significant mass of cold dust: the mean dust mass is 5.5x10^7 Msun, with individual galaxies ranging from 9x10^5-4x10^8 Msun. This is comparable to that of spirals in our sample, and is an order of magnitude more dust than that found for the control ETGs, which have a median dust mass inferred from stacking of (0.8-4.0)x10^6 Msun. The ETGs detected in H-ATLAS have bluer NUV-r colours, higher specific star-formation rates and younger stellar populations than ETGs which are optically selected, and may be transitioning from the blue cloud to the red sequence. We also find that H-ATLAS and control ETGs inhabit similar low-density environments. We conclude that the dust in H-ATLAS and control ETGs cannot be solely from stellar sources, and a large contribution from dust formed in the ISM or external sources is required. Alternatively, dust destruction may not be as efficient as predicted. We also explore the properties of the most passive spiral galaxies in our sample with SSFR<10^-11/yr. We find these passive spirals have lower dust-to-stellar mass ratios, higher stellar masses and older stellar population ages than normal spirals. The passive spirals inhabit low density environments similar to those of the normal spiral galaxies in our sample. This shows that the processes which turn spirals passive do not occur solely in the intermediate density environments of group and cluster outskirts. (Abridged)

astro-ph.CO↗

Herschel-ATLAS Galaxy Counts and High Redshift Luminosity Functions: The Formation of Massive Early Type Galaxies

Exploiting the Herschel-ATLAS Science Demonstration Phase (SDP) survey data, we have determined the luminosity functions (LFs) at rest-frame wavelengths of 100 and 250 micron and at several redshifts z>1, for bright sub-mm galaxies with star formation rates (SFR) >100 M_sun/yr. We find that the evolution of the comoving LF is strong up to z~2.5, and slows down at higher redshifts. From the LFs and the information on halo masses inferred from clustering analysis, we derived an average relation between SFR and halo mass (and its scatter). We also infer that the timescale of the main episode of dust-enshrouded star formation in massive halos (M_H>3*10^12 M_sun) amounts to ~7*10^8 yr. Given the SFRs, which are in the range 10^2-10^3 M_sun/yr, this timescale implies final stellar masses of order of 10^11-10^12 M_sun. The corresponding stellar mass function matches the observed mass function of passively evolving galaxies at z>1. The comparison of the statistics for sub-mm and UV selected galaxies suggests that the dust-free, UV bright phase, is >10^2 times shorter than the sub-mm bright phase, implying that the dust must form soon after the onset of star formation. Using a single reference Spectral Energy Distribution (SED; the one of the z~2.3 galaxy SMM J2135-0102), our simple physical model is able to reproduce not only the LFs at different redshifts > 1 but also the counts at wavelengths ranging from 250 micron to ~1 mm. Owing to the steepness of the counts and their relatively broad frequency range, this result suggests that the dispersion of sub-mm SEDs of z>1 galaxies around the reference one is rather small.

astro-ph.CO↗

Observation of H2O in a strongly lensed Herschel-ATLAS source at z=2.3

The Herschel survey, H-ATLAS, with its large areal coverage, has recently discovered a number of bright, strongly lensed high-z submillimeter galaxies. The strong magnification makes it possible to study molecular species other than CO, which are otherwise difficult to observe in high-z galaxies. Among the lensed galaxies already identified by H-ATLAS, the source J090302.9-014127B (SDP.17b) at z = 2.305 is remarkable due to its excitation conditions and a tentative detection of the H2O 202-111 emission line (Lupu et al. 2010). We report observations of this line in SDP.17b using the IRAM interferometer equipped with its new 277- 371GHz receivers. The H2O line is detected at a redshift of z = 2.3049+/-0.0006, with a flux of 7.8+/-0.5 Jy km s-1 and a FWHM of 250+/-60 km s-1. The new flux is 2.4 times weaker than the previous tentative detection, although both remain marginally consistent within 1.6-sigma. The intrinsic line luminosity and ratio of H2O(202-111)/CO8-7 seem comparable with those of the nearby starburst/enshrouded-AGN Mrk 231, suggesting that SDP.17b could also host a luminous AGN. The detection of a strong H2O 202-111 line in SDP.17b implies an efficient excitation mechanism of the water levels that must occur in very dense and warm interstellar gas.

astro-ph.CO↗

Physical conditions of the interstellar medium of high-redshift, strongly lensed submillimetre galaxies from the Herschel-ATLAS

We present Herschel-SPIRE Fourier Transform Spectrometer (FTS) and radio follow-up observations of two Herschel-ATLAS (H-ATLAS) detected strongly lensed distant galaxies. In one of the targeted galaxies H-ATLAS J090311.6+003906 (SDP.81) we detect [OIII] 88\mum and [CII] 158\mum lines at a signal-to-noise ratio of ~5. We do not have any positive line identification in the other fainter target H-ATLAS J091305.0-005343 (SDP.130). Currently SDP.81 is the faintest sub-mm galaxy with positive line detections with the FTS, with continuum flux just below 200 mJy in the 200-600 \mum wavelength range. The derived redshift of SDP.81 from the two detections is z=3.043 +/-0.012, in agreement with ground-based CO measurements. This is the first detection by Herschel of the [OIII] 88\mum line in a galaxy at redshift higher than 0.05. Comparing the observed lines and line ratios with a grid of photo-dissociation region (PDR) models with different physical conditions, we derive the PDR cloud density n ~ 2000 cm^{-3} and the far-UV ionizing radiation field G_0 ~ 200 (in units of the Habing field -- the local Galactic interstellar radiation field of 1.6x10^{-6} W/m^2). Using the CO derived molecular mass and the PDR properties we estimate the effective radius of the emitting region to be 500-700 pc. These characteristics are typical for star-forming, high redshift galaxies. The radio observations indicate that SDP.81 deviates significantly from the local FIR/radio correlation, which hints that some fraction of the radio emission is coming from an AGN. The constraints on the source size from millimiter-wave observations put a very conservative upper limit of the possible AGN contribution to less than 33%. These indications, together with the high [OIII]/FIR ratio and the upper limit of [OI] 63\mum/[CII] 158\mum suggest that some fraction of the ionizing radiation is likely to originate from an AGN.

astro-ph.CO↗

Herschel-ATLAS: Rapid evolution of dust in galaxies in the last 5 billion years

We present the first direct and unbiased measurement of the evolution of the dust mass function of galaxies over the past 5 billion years of cosmic history using data from the Science Demonstration Phase of the Herschel-ATLAS. The sample consists of galaxies selected at 250μm which have reliable counterparts from SDSS at z < 0.5, and contains 1867 sources. Dust masses are calculated using both a single temperature grey-body model for the spectral energy distribution and also using a model with multiple temperature components. The dust temperature for either model shows no trend with redshift. Splitting the sample into bins of redshift reveals a strong evolution in the dust properties of the most massive galaxies. At z = 0.4 - 0.5, massive galaxies had dust masses about five times larger than in the local Universe. At the same time, the dust-to-stellar mass ratio was about 3-4 times larger, and the optical depth derived from fitting the UV-sub-mm data with an energy balance model was also higher. This increase in the dust content of massive galaxies at high redshift is difficult to explain using standard dust evolution models and requires a rapid gas consumption timescale together with either a more top-heavy IMF, efficient mantle growth, less dust destruction or combinations of all three. This evolution in dust mass is likely to be associated with a change in overall ISM mass, and points to an enhanced supply of fuel for star formation at earlier cosmic epochs.

astro-ph.CO↗

Gas and dust in a submillimeter galaxy at z = 4.24 from the Herschel ATLAS

We report ground-based follow-up observations of the exceptional source, ID141, one the brightest sources detected so far in the H-ATLAS cosmological survey. ID141 was observed using the IRAM 30-meter telescope and Plateau de Bure interferometer (PdBI), the Submillimeter Array (SMA) and the Atacama Pathfinder Experiment (APEX) submillimeter telescope to measure the dust continuum and emission lines of the main isotope of carbon monoxide and carbon ([C I] and [C II]). The detection of strong CO emission lines with the PdBI confirms that ID141 is at high redshift (z=4.243 +/- 0.001). The strength of the continuum and emission lines suggests that ID141 is gravitationally lensed. The width (Delta V (FWHM) ~ 800 km/s}) and asymmetric profiles of the CO and carbon lines indicate orbital motion in a disc or a merger. The properties derived for ID141 are compatible with a ultraluminous (L_FIR ~ 8.5 +/- 0.3 x 10^13/mu_L Lsun, where mu_L is the amplification factor, dense (n ~ 10^4 cm^-3) and warm (T_kin ~ 40K) starburst galaxy, with an estimated star-formation rate of (0.7 to 1.7) x 10^4/mu_L Msun/yr. The carbon emission lines indicate a dense (n ~ 10^4 cm^-3) Photo-Dominated Region, illuminated by a far-UV radiation field a few thousand times more intense than that in our Galaxy. In conclusion, the physical properties of the high-z galaxy, ID141, are remarkably similar to those of local ultraluminous infrared galaxies.

astro-ph.CO↗

The environment and characteristics of low redshift galaxies detected by the Herschel-ATLAS

We investigate the ultraviolet and optical properties and environment of low redshift galaxies detected in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) science demonstration data. We use the Sloan Digital Sky Survey seventh release and the Galaxy And Mass Assembly database to select galaxies with r_Petro < 19.0 mag in the redshift range 0.02 < z < 0.2 and look for their submillimeter counterparts in H-ATLAS. Our results show that at low redshift, H-ATLAS detects mainly blue/star-forming galaxies with a minor contribution from red systems which are highly obscured by dust. In addition we find that the colour of a galaxy rather than the local density of its environment determines whether it is detectable by H-ATLAS. The average dust temperature of galaxies that are simultaneously detected by both PACS and SPIRE is 25K \pm 4K, independent of environment. This analysis provides a glimpse of the potential of the H-ATLAS data to investigate the submillimeter properties of galaxies in the local universe.

astro-ph.CO↗

Herschel-ATLAS: detection of a far-infrared population around galaxy clusters

We report the detection of a significant excess in the surface density of far-infrared sources from the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) within ~1 Mpc of the centres of 66 optically-selected clusters of galaxies in the SDSS with ~0.25. From the analysis of the multiwavelength properties of their counterparts we conclude that the far-infrared emission is associated with dust-obscured star formation and/or active galactic nuclei within galaxies in the clusters themselves. The excess reaches a maximum at a radius of ~0.8 Mpc, where we find 1.0\pm0.3 S_250um>34 mJy sources on average per cluster above what would be expected for random field locations. If the far-infrared emission is dominated by star formation (as opposed to AGN) then this corresponds to an average star formation rate of ~7 M_sun/yr per cluster in sources with L_IR>5d10 L_sun. Although lensed sources make a negligible contribution to the excess signal, a fraction of the sources around the clusters could be gravitationally lensed, and we have identified a sample of potential cases of cluster-lensed Herschel sources that could be targeted in follow-up studies.

astro-ph.CO↗

Herschel-ATLAS: First data release of the Science Demonstration Phase source catalogues

The Herschel-ATLAS is a survey of 550 square degrees with the Herschel Space Observatory in five far--infrared and submillimetre bands. The first data for the survey, observations of a field 4x4 sq. degrees in size, were taken during the Science Demonstration Phase, and reach a 5 sigma noise level of 33 mJy/beam at 250 microns. This paper describes the source extraction methods used to create the corresponding Science Demonstration Phase catalogue, which contains 6876 sources, selected at 250 microns, within ~14 sq. degrees. SPIRE sources are extracted using a new method specifically developed for Herschel data; PACS counterparts of these sources are identified using circular apertures placed at the SPIRE positions. Aperture flux densities are measured for sources identified as extended after matching to optical wavelengths. The reliability of this catalogue is also discussed, using full simulated maps at the three SPIRE bands. These show that a significant number of sources at 350 and 500 microns have undergone flux density enhancements of up to a factor of ~2, due mainly to source confusion. Correction factors are determined for these effects. The SDP dataset and corresponding catalogue will be available from http://www.h-atlas.org/.

astro-ph.IM↗

Herschel-ATLAS: The link between accretion luminosity and star formation in quasar host galaxies

We use the science demonstration field data of the Herschel-ATLAS to study how star formation, traced by the far-infrared Herschel data, is related to both the accretion luminosity and redshift of quasars selected from the Sloan Digital Sky Survey and the 2SLAQ survey. By developing a maximum likelihood estimator to investigate the presence of correlations between the far-infrared and optical luminosities we find evidence that the star-formation in quasar hosts is correlated with both redshift and quasar accretion luminosity. Assuming a relationship of the form L_IR \propto L_QSO^θ (1 + z)^ζ, we find θ = 0.22 +/- 0.08 and ζ = 1.6 +/- 0.4, although there is substantial additional uncertainty in ζ of order +/- 1, due to uncertainties in the host galaxy dust temperature. We find evidence for a large intrinsic dispersion in the redshift dependence, but no evidence for intrinsic dispersion in the correlation between L_QSO and L_IR, suggesting that the latter may be due to a direct physical connection between star formation and black hole accretion. This is consistent with the idea that both the quasar activity and star formation are dependent on the same reservoir of cold gas, so that they are both affected by the influx of cold gas during mergers or heating of gas via feedback processes.

astro-ph.CO↗

GAMA/H-ATLAS: The ultraviolet spectral slope and obscuration in galaxies

We use multiwavelength data from the Galaxy And Mass Assembly (GAMA) and Herschel ATLAS (H-ATLAS) surveys to compare the relationship between various dust obscuration measures in galaxies. We explore the connections between the ultraviolet (UV) spectral slope, $β$, the Balmer decrement, and the far infrared (IR) to $150\,$nm far ultraviolet (FUV) luminosity ratio. We explore trends with galaxy mass, star formation rate (SFR) and redshift in order to identify possible systematics in these various measures. We reiterate the finding of other authors that there is a large scatter between the Balmer decrement and the $β$ parameter, and that $β$ may be poorly constrained when derived from only two broad passbands in the UV. We also emphasise that FUV derived SFRs, corrected for dust obscuration using $β$, will be overestimated unless a modified relation between $β$ and the attenuation factor is used. Even in the optimum case, the resulting SFRs have a significant scatter, well over an order of magnitude. While there is a stronger correlation between the IR to FUV luminosity ratio and $β$ parameter than with the Balmer decrement, neither of these correlations are particularly tight, and dust corrections based on $β$ for high redshift galaxy SFRs must be treated with caution. We conclude with a description of the extent to which the different obscuration measures are consistent with each other as well as the effects of including other galactic properties on these correlations.

astro-ph.CO↗

Spitzer Imaging of Herschel-ATLAS Gravitationally Lensed Submillimeter Sources

We present physical properties of two submillimeter selected gravitationally lensed sources, identified in the Herschel Astrophysical Terahertz Large Area Survey. These submillimeter galaxies (SMGs) have flux densities > 100 mJy at 500 um, but are not visible in existing optical imaging. We fit light profiles to each component of the lensing systems in Spitzer IRAC 3.6 and 4.5 um data and successfully disentangle the foreground lens from the background source in each case, providing important constraints on the spectral energy distributions (SEDs) of the background SMG at rest-frame optical-near-infrared wavelengths. The SED fits show that these two SMGs have high dust obscuration with Av ~4 to 5 and star formation rates of ~100 M_sun/yr. They have low gas fractions and low dynamical masses compared to 850 um selected galaxies.

astro-ph.CO↗

GBT Zpectrometer CO(1-0) Observations of the Strongly-Lensed Submillimeter Galaxies from the Herschel ATLAS

The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) has uncovered a population of strongly-lensed submillimeter galaxies (SMGs). The Zpectrometer instrument on the Green Bank Telescope (GBT) was used to measure the redshifts and constrain the masses of the cold molecular gas reservoirs for two candidate high-redshift lensed sources. We derive CO(1-0) redshifts of z=3.042+/-0.001 and z=2.625+/-0.001, and measure molecular gas masses of (1--3)x10^{10}Msun, corrected for lens amplification and assuming a conversion factor of alhpa=0.8 Msun(K km/s pc^2)^{-1}. We find typical L(IR)/L'(CO) ratios of 120+/-40 and 140+/-50 Lsun (K km/s pc^2)^{-1}, which are consistent with those found for local ULIRGs and other high-redshift SMGs. From analysis of published data, we find no evidence for enhanced L(IR)/L'(CO(1-0)) ratios for the SMG population in comparison to local ULIRGs. The GBT results highlight the power of using the CO lines to derive blind redshifts, which is challenging for the SMG population at optical wavelengths given their high obscuration.

astro-ph.CO↗

Which halos host Herschel-ATLAS galaxies in the local Universe?

We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxies in the SDP field of the Herschel-ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey. In order to obtain robust correlation functions, we restrict the analysis to a subset of 969 out of 6900 H-ATLAS galaxies, which have reliable optical counterparts with r<19.4 mag and well-determined spectroscopic redshifts. The overlap region between the two surveys is 12.6 sq. deg; the matched sample has a median redshift of z ~ 0.2. The cross-correlation of GAMA and H-ATLAS galaxies within this region can be fitted by a power law, with correlation length r_0 ~ 4.63 +/- 0.51 Mpc. Comparing with the corresponding auto-correlation function of GAMA galaxies within the SDP field yields a relative bias (averaged over 2-8 Mpc) of H-ATLAS and GAMA galaxies of b_H/b_G ~ 0.6. Combined with clustering measurements from previous optical studies, this indicates that most of the low redshift H-ATLAS sources are hosted by halos with masses comparable to that of the Milky Way. The correlation function appears to depend on the 250 um luminosity, L_250, with bright (median luminosity νL_250 ~ 1.6 x 10^10 L_sun) objects being somewhat more strongly clustered than faint (νL_250 ~ 4.0 x 10^9 L_sun) objects. This implies that galaxies with higher dust-obscured star formation rates are hosted by more massive halos.

astro-ph.CO↗