arXiv subjects

S. J. Lilly

Publications and source records attributed to S. J. Lilly.

At least 127 records · Page 7Linked to original sources

arXiv2002

The Canada-UK Deep Submillimeter Survey V: The Submillimeter Properties of Lyman-Break Galaxies

We have used 850$μ$m maps obtained as part of the Canada-UK Deep Submillimeter Survey (CUDSS) to investigate the sub-mm properties of Lyman-break galaxies (LBGs). We used three samples of Lyman-break galaxies: two from the Canada-France Deep Fields (CFDF) survey covering CUDSS-14 and CUDSS-3, and one from Steidel and collaborators also covering CUDSS-14. We measure a mean flux from both CFDF LBG samples at a level of $\sim2σ$ of 0.414 $\pm$ 0.263 mJy for CUDSS-03 and 0.382 $\pm$ 0.206 mJy for CUDSS-14, but the Steidel et al. sample is consistent with zero flux. From this we place upper limits on the Lyman-break contribution to the $850μm$ background of $\sim$20%. We have also measured the cross-clustering between the LBGs and SCUBA sources. From this measurement we infer a large clustering amplitude of $r_o$ = 11.5 $\pm$ 3.0 $\pm$ 3.0 $h^{-1}$Mpc for the Steidel et al. sample (where the first error is statistical and the second systematic), $r_o$ = 4.5 $\pm$ 7.0 $\pm$ 5.0 $h^{-1}$Mpc for CFDF-14 and $r_o$ = 7.5 $\pm$ 7.0 $\pm$ 5.0 $h^{-1}$Mpc for CFDF-3. The Steidel et al sample, for which we have most only significant detection of clustering is also the largest of the three samples and has spectroscopically confirmed redshifts.

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arXiv2002

The Gravitational Lens CFRS03.1077

An exquisite gravitational arc with a radius of 2.1" has been discovered around the z = 0.938 field elliptical galaxy CFRS03.1077 during HST observations of Canada-France Redshift Survey (CFRS) fields. Spectroscopic observations of the arc show that the redshift of the resolved lensed galaxy is z = 2.941. This gravitational lens-source system is well-fitted using the position angle and ellipticity derived from the visible matter distribution and an isothermal mass profile with a mass corresponding to sigma =387+-5 km/s. Surprisingly, given the evidence for passive evolution of elliptical galaxies, this is in good agreement with an estimate based on the fundamental plane for z = 0 ellipticals. This, perhaps, indicates that this galaxy has not shared in the significant evolution observed for average elliptical galaxies at z ~ 1. A second elliptical galaxy with similar luminosity from the CFRS survey, CFRS 14.1311 at z=0.807, is also a lens but in this case the lens model gives a much smaller mass-to-light ratio, i.e., it appears to confirm the expected evolution. This suggests that this pair of field elliptical galaxies may have very different evolutionary histories, a significant result if confirmed. Clearly, CFRS03.1077 demonstrates that these "Einstein rings" are powerful probes of high redshift galaxies.

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arXiv2002

The Canada-UK Deep Submillimeter Survey VI: The 3-Hour Field

We present the complete submillimeter data for the Canada-UK Deep Submillimeter Survey (CUDSS) 3-hour field. The obeservations were taken with the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope on Mauna Kea. The 3-hour field is one of two main fields in our survey and covers 60 square arcminutes to a 3-sigma depth of 3 mJy. In this field we have detected 27 sources above 3-sigma and 15 above 3.5-sigma. We assume the source counts follow the form $N(S) {\propto} S^{-α}$ and measure $α$ = 3.3$^{+1.4}_{-1.0}$. This is in good agreement with previous studies and further supports our claim (Eales et al., 2000) that SCUBA sources brighter than 3 mJy produce ~20% of the 850$μ$m background energy. Using preliminary ISO 15 $μ$m maps and VLA 1.4 GHz data we have identified counterparts for six objects and have marginal detections at 450$μ$m for two additional sources. With this information we estimate a median redshift for the sample of 2.0$\pm$0.5, with $\sim$10% lying at $z<$ 1. We have measured the angular clustering of S850 > 3 mJy sources using the source catalogues from the CUDSS two main fields, the 3-hour and 14-hour fields, and find a marginal detection of clustering, primarily from the 14-hour field, of $ω(θ)=4.4\pm2.9 θ^{-0.8}$. This is consistent with clustering at least as strong as that seen for the Lyman-break galaxy population and the Extremely Red Objects. Since SCUBA sources are selected over a broader range in redshifts than these two populations the strength of the true spatial clustering is expected to be correspondingly stronger.

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arXiv2001

The Canada-France deep fields survey-I: 100,000 galaxies, 1 deg^2: a precise measurement of ω(θ) to IAB~25

(abridged) Using the UH8K mosaic camera, we have measured the angular correlation function ω(θ) for 100,000 galaxies over four widely separated fields totalling ~1°^2 and reaching IAB~25.5. With this sample we investigate the dependence of ω(θ) at 1', A_ω(1'), on sample median IAB magnitude in the range 19.5 1. Models with ε~0 cannot simultaneously match both bright and faint measurements of A_ω(1`). We show how this result is a natural consequence of the ``bias-free'' nature of the εformalism and is consistent with the field galaxy population in the range 22.0<IAB<24.0 being dominated by galaxies of low intrinsic luminosity.

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arXiv2000

The Metallicity of 0.5<z<1 Field Galaxies

We have measured the emission line ratios in a sample of 34 CFRS star-forming galaxies with redshifts between 0.5 < z < 1.0, and computed their metallicities by means of the empirically-calibrated R_23 metallicity estimator introduced by Pagel et al. (1979). The current analysis concentrates on the 15 galaxies with L_Hbeta > 1.2x10^41 erg s-1. Although our results can only be regarded as preliminary until near-IR spectroscopy of Halpha and [NII]6583 are available, the metallicities of these galaxies appear to be remarkably similar to those of local galaxies selected in the same way, and there appears to have been little change in the relationship between metallicity and line- and continuum-luminosity from z~1 to today. At this stage our results do not support the idea that these galaxies, known to be generally small and with late-type morphologies, are dwarf galaxies brightened by large bursts of star-formation, as had been suggested from previous studies. Rather, our findings are more consistent with a picture in which these systems are the progenitors of today's massive metal-rich galaxies.

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arXiv2000

High spatial resolution observations of CUDSS14A: a SCUBA-selected Ultraluminous galaxy at high redshift

We present a high-resolution millimetre interferometric image of the brightest SCUBA-selected galaxy from the Canada-UK deep SCUBA survey (CUDSS). We make a very clear detection at 1.3 mm, but fail to resolve any structure in the source. The interferometric position is within 1.5 arcsec of the SCUBA 850 $μ$m centroid, and also within 1.5 arcsec of a 44 $μ$Jy radio source and a very faint, extremely red galaxy which we had previously identified as the submillimetre source. We also present new optical and infrared imaging, and infrared spectroscopy of this source. We model the overall spectral energy distribution and conclude that it lies within the redshift range 2$< z < 4.5$. The submm/FIR luminosity of CUDSS14A is very weakly dependent on redshift within the constrained range, and is roughly 4$\times10^{12}$ L$_\odot$ (for H$_0$=75 and an assumed Arp220-like spectrum), which implies a star-formation rate $\sim$1000 M$_\odot$ yr$^{-1}$. We derive an approximate gas mass of $\sim 10^{10}$ M$_\odot$ which would imply the current star-forming activity cannot be sustained for longer than about 10 million years. With the present data however we are unable to rule out a significant AGN contribution to the total luminosity.

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arXiv1999

Hubble Space Telescope imaging of the CFRS and LDSS redshift surveys - IV. Influence of mergers in the evolution of faint field galaxies from z~1

HST images of a sample of 285 galaxies with measured z from the CFRS and Autofib-LDSS redshift surveys are analysed to derive the evolution of the merger fraction out to z~1. We have performed visual and machine-based merger identifications, as well as counts of bright pairs of galaxies with magnitude differences less than 1.5 mag. We find that the pair fraction increases with z, with up to ~20% of the galaxies being in physical pairs at z~0.75-1. We derive a merger fraction varying with z as (1+z)^{3.2 +/- 0.6}, after correction for line-of-sight contamination, in excellent agreement with the merger fraction derived from the visual classification of mergers for which m = 3.4 +/- 0.6. After correcting for seeing effects on the ground-based selection of survey galaxies, we conclude that the pair fraction evolves as (1+z)^{2.7 +/- 0.6}. This implies that an average L* galaxy will have undergone 0.8 to 1.8 merger events from z=1 to 0, with 0.5 to 1.2 merger events occuring in a 2 Gyr time span at z~0.9. This result is consistent with predictions from semi-analytical models of galaxy formation. From the simple co-addition of the observed luminosities of the galaxies in pairs, physical mergers are computed to lead to a brightening of 0.5 mag for each pair on average, and a boost in star formation rate of a factor of 2, as derived from the average [O II] equivalent widths. Mergers of galaxies are therefore contributing significantly to the evolution of both the luminosity function and luminosity density of the Universe out to z~1.

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arXiv1999

Hubble Space Telescope Imaging of the CFRS and LDSS Redshift Surveys---III. Field elliptical galaxies at 0.2 < z < 1.0

Surface photometry has been performed on a sample of 46 field elliptical galaxies. These galaxies are described well by a deVaucouleurs R^{1/4} profile. The sample was selected from the combined Canada-France and LDSS redshift surveys and spans the range 0.20 < z < 1.00. The relationship between galaxy half-light radius and luminosity evolves such that a galaxy of a given size is more luminous by Delta M_B=-0.97 \pm 0.14 mag at z=0.92 and the mean rest-frame color shifts blueward by Delta (U-V) =-0.68 \pm 0.11 at z=0.92 relative to the local cluster relations. Approximately 1/3 of these elliptical galaxies exhibit [OII] 3727 emission lines with equivalent widths > 15 angstroms indicating ongoing star formation. Estimated star-formation rates imply that \le 5% of the stellar mass in the elliptical galaxy population has been formed since z=1. We see no evidence for a decline in the space density of early-type galaxies with look-back time. The statistics and a comparison with local luminosity functions are both consistent with the view that the population of massive early-type galaxies was largely in place by z~1. This implies that merging is not required since that time to produce the present-day space density of elliptical galaxies.

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arXiv1998

Deep Galaxy survey at 6.75 micron with the ISO satellite

Deep 6.75um mid-IR ISOCAM observations were obtained of the Canada-France Redshift Survey (CFRS) 1415+52 field with the Infrared Space Observatory. The identification of the sources with optical counterparts is described in detail, and a classification scheme is devised which depends on the S/N of the detection and the inverse probability of chance coincidence. 83% of the 54 ISOCAM sources are identified with Iab<23.5 counterparts. The (I-K)ab colors, radio properties, spectrophotometric properties and frequency of nuclear activity of these counterparts differ on average from those of typical CFRS galaxies. CFRS spectra are available for 21 of the sources which have Iab <= 22.5 (including 7 stars). Most of the strongest sources are stars or AGN. Among the non--stellar counterparts with spectra, 40% are AGNs, and 53% are galaxies that display star formation activity and/or significant contributions of A stars. The ISOCAM sources also display an IR excess, even when compared with heavily-reddened local starburst galaxies. An upper limit of 30% of extragalactic ISO sources could be at z>1 of the 44 S6.75um > 150uJy sources which are non-stellar (7 "spectroscopic" and 3 "photometric" stars excluded)

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arXiv1998

15um ISO observations of a CFRS field: the cosmic SFR as derived from UV, optical, mid-IR and radio photometry

The CFRS 1452+52 field has been deeply imaged with the Infrared Space Observatory (ISO) using ISOCAM through the LW3 filter (12-18um). Careful data analysis and comparison to deep optical and radio data have allowed us to generate a catalog of 78 15um sources with both radio and optical identifications. They are redder and lie at higher redshift than I-band selected galaxies, with most of them being star-forming galaxies. We have considered the galaxies detected at radio and 15$μ$m wavelengths which potentially include all strong and heavily extincted starbursts, up to z=1. Spectral energy distributions (SED) for each of the sources have been derived using deep radio, mid-IR, near-IR, optical and UV photometry. The sources were then spectrally classified by comparing to SEDs of well known nearby galaxies. By deriving their FIR luminosities by interpolation, we can estimate their Star Formation Rate (SFR) in a way which does not depend sensitively on the extinction. 75% (-40%, +10%) of the star formation at $z \le 1$ is related to IR emission and the global extinction is in the range Av=0.5 -- 0.85. While heavily extincted starbursts, with SFR in excess of 100 Mo/yr constitute less than a percent of all galaxies, they contribute about 18% of the SFR density out to z=1. Their morphologies range from S0 to Sab, and more than a third are interacting systems. The SFR derived by FIR fluxes is likely to be ~2.9 times higher than those previously estimated from UV fluxes. The derived stellar mass formed since the redshift of 1 could be too high when compared to the present day stellar mass density. This might be due to an IMF in distant star-forming galaxies different from the solar neighborhood one, or to an underestimate of the local stellar mass density.

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arXiv1997

HST imaging of CFRS and LDSS galaxies - I: Morphological Properties

(Abridged) We analyse Hubble Space Telescope images of a complete sample of 341 galaxies drawn from both the Canada France and Autofib/Low Dispersion Survey Spectrograph ground-based redshift surveys. We discuss morphological classifications of these galaxies, and quantify possible biases that may arise from various redshift-dependent effects. We then discuss these biases in the context of automated classifications, and quantify the expected misclassification in our system. After allowing for such biases, the redshift distribution for normal spirals, together with their luminosity function derived as a function of redshift, indicates approximately 1 magnitude of luminosity evolution in B(AB) by z=1. The elliptical sample is too small for precise evolutionary constraints. However, we find a substantial increase in the proportion of galaxies with irregular morphology at large redshift. These galaxies also appear to be the dominant cause of the rapid rise with redshift in the blue luminosity density identified in the redshift surveys. Although galaxies with irregular morphology may well comprise a mixture of different physical systems and might not correspond to present day irregulars, it is clear that the apparently declining abundance and luminosities of our distant ``irregulars'' holds an important key to understanding recent evolution in the star formation history of normal galaxies.

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arXiv1997

Hubble Space Telescope imaging of the CFRS and LDSS redshift surveys II: Structural parameter and the evolution of disk galaxies to z=1

(Abridged) Several aspects of the evolution of star-forming galaxies are studied using measures of the 2-dimensional surface brightness profile of a sample of 341 faint objects selected from the CFRS and LDSS redshift surveys that have been observed with the Hubble Space Telescope. The size function of disk scale lengths in disk-dominated galaxies is found to stay roughly constant to z=1. This result, which is strengthened by inclusion of the local de Jong et al (1996) size function, suggests that the scale lengths of typical disks can not have grown substantially with cosmic epoch since z=1, unless a corresponding number of large disks have been destroyed through merging. In addition to a roughly constant number density, the galaxies with large disks have, as a set, properties consistent with the idea that they are similar galaxies observed at different cosmic epochs. However, on average, they show higher B-band disk surface brightnesses, bluer overall (U-V) colors, higher [OII] 3727 equivalent widths and less regular morphologies at high redshift than at low redshift, suggesting an increase in the star-formation rate by a factor of about 3 to z=0.7. This is consistent with the expectations of recent models for the evolution of the disk of the Milky Way and similar galaxies. The evolution of the large disk galaxies is probably not sufficient to account for the evolution of the overall luminosity function of galaxies over the interval 0<z<1, especially if Omega=1. Analysis of the half-light radii of all the galaxies in the sample and construction of the bivariate size-luminosity function suggests that larger changes in the galaxy population are due to smaller galaxies, those with half-light radii around 5 h_{50}^{-1} kpc

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arXiv1996

CFRS XIV: Spectral Properties Of Field Galaxies Up To z = 1

The spectral properties of more than 400 CFRS galaxies and their changes over the redshift interval 0 - 1.3 are investigated. Emission line intensities and equivalent widths for accessible lines have been measured, as well as continuum color indices based on 200A wide spectral regions. Within the CFRS sample, the comoving fraction of galaxies with significant emission lines (EW(OII) > 15A) increases from ~13% locally to over 50% at z > 0.5. The fraction of luminous ( M_{B} < -20) quiescent galaxies (those without [OII] 3727 emission) decreases with redshift from 53% at z = 0.3 to 23% at z > 0.5, the latter fraction being similar to that of early type galaxies at that redshift. There is considerable evidence in the data presented here that star formation increases from z = 0 to z > 0.5 in disk galaxies. However, the absence of extremely blue colors and the presence of significant Balmer absorption suggests that the star formation is primarily taking place over long periods of time, rather than in short-duration, high-amplitude ``bursts''. There are several indications that the average metallicity and dust opacity were lower in emission-line galaxies at high redshift than those typically seen in luminous galaxies locally. Beyond z = 0.7, almost all the emission-line galaxies, including the most luminous (at 1mu at rest) ones, have colors approaching those of present-day irregular galaxies, and a third of them have indications (primarily from the strength of the 4000A break) of metallicities significantly less than solar (Z < 0.2 Z_{sun}). (abbreviated)

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arXiv1996

The Canada-France Redshift Survey XII: Nature of emission-line field galaxy population up to z = 0.3

We present a spectroscopic study of the 138 field galaxies to a redshift z = 0.3 from the I-selected Canada-France Redshift Survey. 117(85%) spectra exhibit at least H alpha in emission, the remaining 21(15%) are purely absorption-line spectra. We focus our analysis on spectra with H alpha and H beta in emission, accounting for about half of this low-z sample, which we classify using emission-line ratio diagrams. Using photoionization models, we determine the extreme boundaries of H II galaxies in these diagnostic diagrams, and demonstrate that the emission-line ratios of a significant fraction of galaxies require harder photoionization sources than massive O stars. We find that about 17% of the field galaxies have emission-line ratios consistent with active galaxies, e.g., Seyfert 2 or LINERs. After correcting for stellar absorption under the Balmer lines, we conclude that the fraction of such galaxies is at least 8% of the field galaxy population at z < 0.3.

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arXiv1996

The gravitational lens CFRS14.1311 = HST 14176+5226

Ratnatunga et al. (1995) have recently proposed that an object, HST 14176+5226, in the "Groth-Westphal" HST survey strip is an "Einstein cross" gravitational lens. By chance, this object has been previously observed in the Canada-France Redshift Survey. The candidate lens, catalogued as CFRS14.1311, is an elliptical galaxy at z = 0.81. In addition, the spectrum shows a strong, spatially-extended, emission feature at 5342A that almost certainly originates from two of the four "lensed" images. We tentatively identify this emission line as Ly alpha at z =3.4. A less prominent emission feature at 6822A may be C IV 1549. Our data thus support the identification of this system as a new quadruple-image lens.

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arXiv1996

The CANADA-FRANCE REDSHIFT SURVEY XI: Morphology of high-redshift field galaxies from high-resolution ground-based imaging

The 143 galaxies with secure redshifts (median z = 0.62) from the 1415+52 field of the Canada-France Redshift Survey have been imaged at CFHT with median seeing of 0.67 arcseconds. Structural parameters have been derived by fitting multi-component models, and the results confirm two phenomena seen in a smaller sample of galaxies imaged with HST. First, 11% of the galaxies lie off the normal locus of colour vs. bulge fraction. This class of objects ("blue-nucleated galaxies" or BNGs) was first identified using HST observations (Schade et al. 1995, Ap J, 451, L1), where it was shown that they are associated with peculiar or asymmetric structures and mergers/interactions. The observed frequency of BNGs in this sample is 14% for 0.5 < z < 1.2 and 6% at 0.2 < z < 0.5, but the true frequency is likely to be a factor ~2 higher after corrections are made for the effect of asymmetric/peculiar structures. Second, galaxy disks at 0.5 < z < 1.1 are found to have a mean rest-frame, inclination-corrected, central surface brightness of $μ_{AB}(B)=19.8 \pm 0.1$ mag arcsec$^{-2}$, about 1.6 mag brighter than the Freeman (1970) value. At low redshift, the mean surface brightness is consistent with the Freeman value. These results are consistent with the HST observations. With larger numbers of galaxies and therefore more statistical weight, they demonstrate the capabilities, and limits, of ground-based work in the study of galaxy morphology at high redshift.

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arXiv1996

The CANADA-FRANCE REDSHIFT SURVEY XIII: The luminosity density and star-formation history of the Universe to z ~ 1

The comoving luminosity density of the Universe is estimated from the CFRS faint galaxy sample in three wavebands (2800A, 4400A and 1 micron) over the redshift range 0 < z < 1. In all three wavebands, the comoving luminosity density increases markedly with redshift. For a (q_0 = 0.5, Omega = 1.0) cosmological model, the comoving luminosity density increases as $(1+z)^{2.1 \pm 0.5}$ at 1 micron, as $(1+z)^{2.7 \pm 0.5}$ at 4400A and as $(1+z)^{3.9 \pm 0.75}$ at 2800A, these exponents being reduced by 0.43 and 1.12 for (0.05,0.1) and (-0.85,0.1) cosmological models respectively. The variation of the luminosity density with epoch can be reasonably well modelled by an actively evolving stellar population with a Salpeter initial mass function (IMF) extending to 125 M_sun, a star-formation rate declining with a power 2.5, and a turn-on of star-formation at early epochs. A Scalo (1986) IMF extending to the same mass limit produces too many long-lived low mass stars. This rapid evolution of the star-formation rate and comoving luminosity density of the Universe is in good agreement with the conclusions of Pei and Fall (1995) from their analysis of the evolving metallicity of the Universe. One consequence of this evolution is that the physical luminosity density at short wavelengths has probably declined by two orders of magnitude since z ~ 1.

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arXiv1995

The Canada France Redshift Survey VIII: Evolution of the clustering of galaxies from z~1

We have used the projected two-point correlation function, $w(r_p)$, to investigate the spatial distribution of the 591 galaxies with secure redshifts between $0 \leq z \leq 1.3$ in the five CFRS fields. The slope of the two-point correlation function for the sample as a whole is $γ=1.64\pm0.05$, very similar to the local slope, and $γ$ is therefore not strongly evolving with redshift. However, the amplitude of the correlation function decreases strongly with increasing redshift, so that at $z\approx0.6$ it is a factor of 10 lower (for $q_0=0.5$) than for a similarly-selected local galaxy population, on scales $0.1<r<2h^{-1}$ Mpc ($q_0=0.5$). As a whole, the CFRS data is adequately represented by $r_0(z=0.53)=1.33 \pm 0.09 h^{-1}$Mpc for $q_0=0.5$, and $r_0(z=0.53)=1.57 \pm 0.09 h^{-1}$Mpc for $q_0=0$. Unless the galaxy population at high redshift is quite different from any population seen locally, an unlikely possibility, then this implies growth of clustering as described by the evolutionary parameter $ε$ to be between $0 < ε< +2$. No difference in the clustering of red and blue galaxies is seen at $z \geq 0.5$, although at lower redshifts, $0.2 \leq z \leq 0.5$, blue galaxies are somewhat less strongly correlated than the redder galaxies, as seen in local samples. This effect could be the equivalent for field galaxies to the Butcher-Oemler effect seen in clusters of galaxies. The cross-correlation functions between red and blue samples have comparable amplitudes to the auto-correlation functions of each. The distribution and power spectrum of pair separations does not indicate

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