Search

We present the results of a novel new search of the first data-release from the Sloan Digital Sky Survey(SDSS-DR1) for the spectra of supernovae. The use of large spectroscopic galaxy surveys offers the prospect of obtaining improved estimates of the local supernova rate, with the added benefit of a very different selection function to that of conventional photometric surveys. In this Letter we present an overview of our search methodology and the details of 19 Type Ia supernovae found in SDSS-DR1. The supernovae sample is used to make a preliminary estimate Gamma_Ia = 0.4 +- 0.2h2 SNu, of the cosmological SNe rate.

We present the results of a novel new search of the first data-release from the Sloan Digital Sky Survey(SDSS-DR1) for the spectra of supernovae. The use of large spectroscopic galaxy surveys offers the prospect of obtaining improved estimates of the local supernova rate, with the added benefit of a very different selection function to that of conventional photometric surveys. In this Letter we present an overview of our search methodology and the details of 19 Type Ia supernovae found in SDSS-DR1. The supernovae sample is used to make a preliminary estimate Gamma_Ia = 0.4 +- 0.2h2 SNu, of the cosmological SNe rate.

We describe the design and data sample from the DEEP2 Galaxy Redshift Survey, the densest and largest precision-redshift survey of galaxies at z ~ 1 completed to date. The survey has conducted a comprehensive census of massive galaxies, their properties, environments, and large-scale structure down to absolute magnitude M_B = -20 at z ~ 1 via ~90 nights of observation on the DEIMOS spectrograph at Keck Observatory. DEEP2 covers an area of 2.8 deg^2 divided into four separate fields, observed to a limiting apparent magnitude of R_AB=24.1. Objects with z < 0.7 are rejected based on BRI photometry in three of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted ~2.5 times more efficiently than in a purely magnitude-limited sample. Approximately sixty percent of eligible targets are chosen for spectroscopy, yielding nearly 53,000 spectra and more than 38,000 reliable redshift measurements. Most of the targets which fail to yield secure redshifts are blue objects that lie beyond z ~ 1.45. The DEIMOS 1200-line/mm grating used for the survey delivers high spectral resolution (R~6000), accurate and secure redshifts, and unique internal kinematic information. Extensive ancillary data are available in the DEEP2 fields, particularly in the Extended Groth Strip, which has evolved into one of the richest multiwavelength regions on the sky. DEEP2 surpasses other deep precision-redshift surveys at z ~ 1 in terms of galaxy numbers, redshift accuracy, sample number density, and amount of spectral information. We also provide an overview of the scientific highlights of the DEEP2 survey thus far. This paper is intended as a handbook for users of the DEEP2 Data Release 4, which includes all DEEP2 spectra and redshifts, as well as for the publicly-available DEEP2 DEIMOS data reduction pipelines. [Abridged], Comment: submitted to ApJS; data products available for download at http://deep.berkeley.edu/DR4

We describe the design and data sample from the DEEP2 Galaxy Redshift Survey, the densest and largest precision-redshift survey of galaxies at z ~ 1 completed to date. The survey has conducted a comprehensive census of massive galaxies, their properties, environments, and large-scale structure down to absolute magnitude M_B = -20 at z ~ 1 via ~90 nights of observation on the DEIMOS spectrograph at Keck Observatory. DEEP2 covers an area of 2.8 deg^2 divided into four separate fields, observed to a limiting apparent magnitude of R_AB=24.1. Objects with z < 0.7 are rejected based on BRI photometry in three of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted ~2.5 times more efficiently than in a purely magnitude-limited sample. Approximately sixty percent of eligible targets are chosen for spectroscopy, yielding nearly 53,000 spectra and more than 38,000 reliable redshift measurements. Most of the targets which fail to yield secure redshifts are blue objects that lie beyond z ~ 1.45. The DEIMOS 1200-line/mm grating used for the survey delivers high spectral resolution (R~6000), accurate and secure redshifts, and unique internal kinematic information. Extensive ancillary data are available in the DEEP2 fields, particularly in the Extended Groth Strip, which has evolved into one of the richest multiwavelength regions on the sky. DEEP2 surpasses other deep precision-redshift surveys at z ~ 1 in terms of galaxy numbers, redshift accuracy, sample number density, and amount of spectral information. We also provide an overview of the scientific highlights of the DEEP2 survey thus far. This paper is intended as a handbook for users of the DEEP2 Data Release 4, which includes all DEEP2 spectra and redshifts, as well as for the publicly-available DEEP2 DEIMOS data reduction pipelines. [Abridged], Comment: submitted to ApJS; data products available for download at http://deep.berkeley.edu/DR4

We study the mean environment of galaxies in the DEEP2 Galaxy Redshift Survey as a function of rest-frame color, luminosity, and [OII] equivalent width. The local galaxy overdensity for >14,000 galaxies at 0.75 < z < 1.35 is estimated using the projected 3rd-nearest-neighbor surface density. Of the galaxy properties studied, mean environment is found to depend most strongly on galaxy color; all major features of the correlation between mean overdensity and rest-frame color observed in the local universe were already in place at z ~ 1. In contrast to local results, we find a substantial slope in the mean dependence of environment on luminosity for blue, star-forming galaxies at z ~ 1, with brighter blue galaxies being found on average in regions of greater overdensity. We discuss the roles of galaxy clusters and groups in establishing the observed correlations between environment and galaxy properties at high redshift, and we also explore the evidence for a ``downsizing of quenching'' from z ~ 1 to z ~ 0. Our results add weight to existing evidence that the mechanism(s) that result in star-formation quenching are efficient in group environments as well as clusters. This work is the first of its kind at high redshift and represents the first in a series of papers addressing the role of environment in galaxy formation at 0 < z < 1., Comment: 36 pages including 10 figures and revised text, accepted to MNRAS

We study the mean environment of galaxies in the DEEP2 Galaxy Redshift Survey as a function of rest-frame color, luminosity, and [OII] equivalent width. The local galaxy overdensity for >14,000 galaxies at 0.75 < z < 1.35 is estimated using the projected 3rd-nearest-neighbor surface density. Of the galaxy properties studied, mean environment is found to depend most strongly on galaxy color; all major features of the correlation between mean overdensity and rest-frame color observed in the local universe were already in place at z ~ 1. In contrast to local results, we find a substantial slope in the mean dependence of environment on luminosity for blue, star-forming galaxies at z ~ 1, with brighter blue galaxies being found on average in regions of greater overdensity. We discuss the roles of galaxy clusters and groups in establishing the observed correlations between environment and galaxy properties at high redshift, and we also explore the evidence for a ``downsizing of quenching'' from z ~ 1 to z ~ 0. Our results add weight to existing evidence that the mechanism(s) that result in star-formation quenching are efficient in group environments as well as clusters. This work is the first of its kind at high redshift and represents the first in a series of papers addressing the role of environment in galaxy formation at 0 < z < 1., Comment: 36 pages including 10 figures and revised text, accepted to MNRAS

We study the applicability of several galaxy environment measures (n^th-nearest-neighbor distance, counts in an aperture, and Voronoi volume) within deep redshift surveys. Mock galaxy catalogs are employed to mimic representative photometric and spectroscopic surveys at high redshift (z ~ 1). We investigate the effects of survey edges, redshift precision, redshift-space distortions, and target selection upon each environment measure. We find that even optimistic photometric redshift errors (\sigma_z = 0.02) smear out the line-of-sight galaxy distribution irretrievably on small scales; this significantly limits the application of photometric redshift surveys to environment studies. Edges and holes in a survey field dramatically affect the estimation of environment, with the impact of edge effects depending upon the adopted environment measure. These edge effects considerably limit the usefulness of smaller survey fields (e.g. the GOODS fields) for studies of galaxy environment. In even the poorest groups and clusters, redshift-space distortions limit the effectiveness of each environment statistic; measuring density in projection (e.g. using counts in a cylindrical aperture or a projected n^th-nearest-neighbor distance measure) significantly improves the accuracy of measures in such over-dense environments. For the DEEP2 Galaxy Redshift Survey, we conclude that among the environment estimators tested the projected n^th-nearest-neighbor distance measure provides the most accurate estimate of local galaxy density over a continuous and broad range of scales., Comment: 17 pages including 16 figures, accepted to ApJ

We study the applicability of several galaxy environment measures (n^th-nearest-neighbor distance, counts in an aperture, and Voronoi volume) within deep redshift surveys. Mock galaxy catalogs are employed to mimic representative photometric and spectroscopic surveys at high redshift (z ~ 1). We investigate the effects of survey edges, redshift precision, redshift-space distortions, and target selection upon each environment measure. We find that even optimistic photometric redshift errors (\sigma_z = 0.02) smear out the line-of-sight galaxy distribution irretrievably on small scales; this significantly limits the application of photometric redshift surveys to environment studies. Edges and holes in a survey field dramatically affect the estimation of environment, with the impact of edge effects depending upon the adopted environment measure. These edge effects considerably limit the usefulness of smaller survey fields (e.g. the GOODS fields) for studies of galaxy environment. In even the poorest groups and clusters, redshift-space distortions limit the effectiveness of each environment statistic; measuring density in projection (e.g. using counts in a cylindrical aperture or a projected n^th-nearest-neighbor distance measure) significantly improves the accuracy of measures in such over-dense environments. For the DEEP2 Galaxy Redshift Survey, we conclude that among the environment estimators tested the projected n^th-nearest-neighbor distance measure provides the most accurate estimate of local galaxy density over a continuous and broad range of scales., Comment: 17 pages including 16 figures, accepted to ApJ

We present the results of a novel new search of the first data-release from the Sloan Digital Sky Survey (SDSS-DR1) for the spectra of supernovae. The use of large spectroscopic galaxy surveys offers the prospect of obtaining improved estimates of the local supernova rate, with the added benefit of a very different selection function to that of conventional photometric surveys. In this Letter we present an overview of our search methodology and the details of 19 Type Ia supernovae found in SDSS--DR1. The supernovae sample is used to make a preliminary estimate, Gamma_Ia = 0.4 +/- 0.2 h^2 SNu, of the cosmological SNe rate., Comment: Accepted for publication in ApJ Letters. Additional information and figures are available at http://supernova.lbl.gov/sdss/ (Note, web address updated)

The DEEP2 Galaxy Redshift Survey is now well underway, having already measured the redshifts to ~5600 galaxies in its first season of observations. Here I briefly review the survey itself, before discussing in more detail some of the initial science results to have recently appeared in the literature. In particular, the potential of the survey to characterize galaxy evolution is discussed, with special emphasis on the role of spectral classification. Some of the applications of this classification, namely to the quantification of galaxy clustering and the measurement of galaxy environments are also discussed here., Comment: Invited review talk at Recontres de Blois, June 2003

We use the latest observations from the 2dF Galaxy Redshift Survey to fit the conditional luminosity function (CLF) formulation of the halo-model for galaxies at z=0. This fit is then used to test the extent of evolution in the halo occupation distribution (HOD) to z=0.8, by comparing the predicted clustering from this CLF to preliminary results from the DEEP2 Redshift Survey. We show that the current observations from the DEEP2 Redshift Survey are remarkably consistent with no evolution in the CLF from z=0 to z=0.8. This result is surprising, in that it suggests that there has been very little change in the way galaxies occupy their host dark matter halos over half the age of the Universe. We discuss in detail the observational constraints we have adopted and also the various different selection effects in each survey and how these impact on the galaxy populations encountered in each survey., Comment: 11 pages, 5 figures. Minor modifications to match version accepted by ApJ

We measure the two-point correlation function xi(r) using a sample of 2219 galaxies in an area of 0.32 degrees^2 at z=0.7-1.35 from the first season of the DEEP2 Galaxy Redshift Survey. We find that xi(r) can be approximated by a power-law, xi(r)=(r/r_0)^-gamma, on scales 0.1-20 Mpc/h. In a sample with an effective redshift of z_eff=0.82, for a Lcdm cosmology we find r_0=3.53 +/-0.81 Mpc/h (comoving) and gamma=1.66 +/-0.12, while in a higher-redshift sample with z_eff=1.14 we find r_0=3.14 +/-0.72 Mpc/h and gamma=1.61 +/-0.11. We find that red, absorption-dominated, passively-evolving galaxies have a larger clustering scale length, r_0, and more prominent ``fingers of God'' than blue, emission-line, actively star-forming galaxies. Intrinsically brighter galaxies also cluster more strongly than fainter galaxies at z~1, with a significant luminosity-bias seen for galaxies fainter than M*. Our results are suggestive of evolution in the galaxy clustering within our survey volume and imply that the DEEP2 galaxies, with a median brightness one magnitude fainter than M* have an effective bias b=0.97 +/-0.13 if sigma_{8 DM}=1 today or b=1.20 +/-0.16 if sigma_{8 DM}=0.8 today. Given the strong luminosity-dependence in the bias that we measure at z~1, the galaxy bias at M* may be significantly greater. We note that our star-forming sample at z~1 has very similar selection criteria as the Lyman-break galaxies at z~3 and that our red, absorption-line sample displays a clustering strength comparable to the expected clustering of the Lyman-break galaxy descendants at z~1. Our results demonstrate that the clustering properties in the galaxy distribution seen in the local Universe were largely in place by z~1., Comment: 17 pages, 8 figures, Revised version accepted by ApJ, minor changes to text and figures

We present a Principal Component Analysis (PCA)-based spectral classification, eta, for the first 5600 galaxies observed in the DEEP2 Redshift Survey. This parameter provides a very pronounced separation between absorption and emission dominated galaxy spectra - corresponding to passively evolving and actively star-forming galaxies in the survey respectively. In addition it is shown that despite the high resolution of the observed spectra, this parameter alone can be used to quite accurately reconstruct any given galaxy spectrum, suggesting there are not many `degrees of freedom' in the observed spectra of this galaxy population. It is argued that this form of classification, eta, will be particularly valuable in making future comparisons between high and low-redshift galaxy surveys for which very large spectroscopic samples are now readily available, particularly when used in conjunction with high-resolution spectral synthesis models which will be made public in the near future. We also discuss the relative advantages of this approach to distant galaxy classification compared to other methods such as colors and morphologies. Finally, we compare the classification derived here with that adopted for the 2dF Galaxy Redshift Survey and in so doing show that the two systems are very similar. This will be particularly useful in subsequent analyses when making comparisons between results from each of these surveys to study evolution in the galaxy populations and large-scale structure., Comment: 10 pages, 9 figures, Accepted for publication in ApJ

We present the results of a novel new search of the first data-release from the Sloan Digital Sky Survey (SDSS-DR1) for the spectra of supernovae. The use of large spectroscopic galaxy surveys offers the prospect of obtaining improved estimates of the local supernova rate, with the added benefit of a very different selection function to that of conventional photometric surveys. In this Letter we present an overview of our search methodology and the details of 19 Type Ia supernovae found in SDSS--DR1. The supernovae sample is used to make a preliminary estimate, Gamma_Ia = 0.4 +/- 0.2 h^2 SNu, of the cosmological SNe rate., Comment: Accepted for publication in ApJ Letters. Additional information and figures are available at http://supernova.lbl.gov/sdss/ (Note, web address updated)

The DEEP2 Galaxy Redshift Survey is now well underway, having already measured the redshifts to ~5600 galaxies in its first season of observations. Here I briefly review the survey itself, before discussing in more detail some of the initial science results to have recently appeared in the literature. In particular, the potential of the survey to characterize galaxy evolution is discussed, with special emphasis on the role of spectral classification. Some of the applications of this classification, namely to the quantification of galaxy clustering and the measurement of galaxy environments are also discussed here., Comment: Invited review talk at Recontres de Blois, June 2003

We use the latest observations from the 2dF Galaxy Redshift Survey to fit the conditional luminosity function (CLF) formulation of the halo-model for galaxies at z=0. This fit is then used to test the extent of evolution in the halo occupation distribution (HOD) to z=0.8, by comparing the predicted clustering from this CLF to preliminary results from the DEEP2 Redshift Survey. We show that the current observations from the DEEP2 Redshift Survey are remarkably consistent with no evolution in the CLF from z=0 to z=0.8. This result is surprising, in that it suggests that there has been very little change in the way galaxies occupy their host dark matter halos over half the age of the Universe. We discuss in detail the observational constraints we have adopted and also the various different selection effects in each survey and how these impact on the galaxy populations encountered in each survey., Comment: 11 pages, 5 figures. Minor modifications to match version accepted by ApJ

We measure the two-point correlation function xi(r) using a sample of 2219 galaxies in an area of 0.32 degrees^2 at z=0.7-1.35 from the first season of the DEEP2 Galaxy Redshift Survey. We find that xi(r) can be approximated by a power-law, xi(r)=(r/r_0)^-gamma, on scales 0.1-20 Mpc/h. In a sample with an effective redshift of z_eff=0.82, for a Lcdm cosmology we find r_0=3.53 +/-0.81 Mpc/h (comoving) and gamma=1.66 +/-0.12, while in a higher-redshift sample with z_eff=1.14 we find r_0=3.14 +/-0.72 Mpc/h and gamma=1.61 +/-0.11. We find that red, absorption-dominated, passively-evolving galaxies have a larger clustering scale length, r_0, and more prominent ``fingers of God'' than blue, emission-line, actively star-forming galaxies. Intrinsically brighter galaxies also cluster more strongly than fainter galaxies at z~1, with a significant luminosity-bias seen for galaxies fainter than M*. Our results are suggestive of evolution in the galaxy clustering within our survey volume and imply that the DEEP2 galaxies, with a median brightness one magnitude fainter than M* have an effective bias b=0.97 +/-0.13 if sigma_{8 DM}=1 today or b=1.20 +/-0.16 if sigma_{8 DM}=0.8 today. Given the strong luminosity-dependence in the bias that we measure at z~1, the galaxy bias at M* may be significantly greater. We note that our star-forming sample at z~1 has very similar selection criteria as the Lyman-break galaxies at z~3 and that our red, absorption-line sample displays a clustering strength comparable to the expected clustering of the Lyman-break galaxy descendants at z~1. Our results demonstrate that the clustering properties in the galaxy distribution seen in the local Universe were largely in place by z~1., Comment: 17 pages, 8 figures, Revised version accepted by ApJ, minor changes to text and figures

We present a Principal Component Analysis (PCA)-based spectral classification, eta, for the first 5600 galaxies observed in the DEEP2 Redshift Survey. This parameter provides a very pronounced separation between absorption and emission dominated galaxy spectra - corresponding to passively evolving and actively star-forming galaxies in the survey respectively. In addition it is shown that despite the high resolution of the observed spectra, this parameter alone can be used to quite accurately reconstruct any given galaxy spectrum, suggesting there are not many `degrees of freedom' in the observed spectra of this galaxy population. It is argued that this form of classification, eta, will be particularly valuable in making future comparisons between high and low-redshift galaxy surveys for which very large spectroscopic samples are now readily available, particularly when used in conjunction with high-resolution spectral synthesis models which will be made public in the near future. We also discuss the relative advantages of this approach to distant galaxy classification compared to other methods such as colors and morphologies. Finally, we compare the classification derived here with that adopted for the 2dF Galaxy Redshift Survey and in so doing show that the two systems are very similar. This will be particularly useful in subsequent analyses when making comparisons between results from each of these surveys to study evolution in the galaxy populations and large-scale structure., Comment: 10 pages, 9 figures, Accepted for publication in ApJ

The correlation between a galaxy's morphology and its observed optical spectrum is investigated. As an example, 4000 galaxies from the 2dF Galaxy Redshift Survey, which possess both good quality spectra and have visually determined morphologies are analysed. Of particular use is the separation of Early and Late type galaxies present in a redshift survey since these can then be used in their respective redshift-independent distance estimators (Dn-sigma and Tully-Fisher). It is determined that galaxies in this sample can be relatively successfully separated into these two types by the use of various statistical methods. These methods are briefly outlined in this paper and are also compared to the default 2dFGRS spectral classification (eta). In addition it is found that the 4000Ang break in the spectrum is the best discriminant in determining its morphological type., Comment: LaTex, 12 pages, 11 figures. Accepted for publication in MNRAS

The 100,000 spectra from the 2 degree Field Galaxy Redshift Survey (2dFGRS) in the 100k Public Data Release represent the largest single compilation of galaxy spectra available. By virtue of its sheer size and the properties of the photometric catalogue that defines the sample, the 2dFGRS is expected to contain a number of potentially interesting objects other than galaxies. A search of the spectra in the 100k Data Release results in a census of 55 candidate high-redshift (z > 0.3) quasars. One additional 2dFGRS spectrum of a low-redshift galaxy shows an apparent anomalous broad emission feature perhaps indicating the presence of a gravitationally lensed quasar. These objects have been identified primarily using two automated routines that we have developed specifically for this task, one of which uses a matched filter and the other a wavelet transform. A number of the quasar images possess complicated morphologies, suggesting the presence of either diffuse foreground objects along the line-of-sight or very nearby point sources. The quasar catalogue will form a target list for future absorption and lensing studies, as well as providing an assessment of the loss of quasars with non-stellar images from the companion 2dF QSO Redshift Survey., Comment: Latex 13 pages, 8 figures. Accepted for publication in MNRAS

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The correlation between a galaxy's morphology and its observed optical spectrum is investigated. As an example, 4000 galaxies from the 2dF Galaxy Redshift Survey, which possess both good quality spectra and have visually determined morphologies are analysed. Of particular use is the separation of Early and Late type galaxies present in a redshift survey since these can then be used in their respective redshift-independent distance estimators (Dn-sigma and Tully-Fisher). It is determined that galaxies in this sample can be relatively successfully separated into these two types by the use of various statistical methods. These methods are briefly outlined in this paper and are also compared to the default 2dFGRS spectral classification (eta). In addition it is found that the 4000Ang break in the spectrum is the best discriminant in determining its morphological type., Comment: LaTex, 12 pages, 11 figures. Accepted for publication in MNRAS

The 100,000 spectra from the 2 degree Field Galaxy Redshift Survey (2dFGRS) in the 100k Public Data Release represent the largest single compilation of galaxy spectra available. By virtue of its sheer size and the properties of the photometric catalogue that defines the sample, the 2dFGRS is expected to contain a number of potentially interesting objects other than galaxies. A search of the spectra in the 100k Data Release results in a census of 55 candidate high-redshift (z > 0.3) quasars. One additional 2dFGRS spectrum of a low-redshift galaxy shows an apparent anomalous broad emission feature perhaps indicating the presence of a gravitationally lensed quasar. These objects have been identified primarily using two automated routines that we have developed specifically for this task, one of which uses a matched filter and the other a wavelet transform. A number of the quasar images possess complicated morphologies, suggesting the presence of either diffuse foreground objects along the line-of-sight or very nearby point sources. The quasar catalogue will form a target list for future absorption and lensing studies, as well as providing an assessment of the loss of quasars with non-stellar images from the companion 2dF QSO Redshift Survey., Comment: Latex 13 pages, 8 figures. Accepted for publication in MNRAS

We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey and by the latest measurements of the Cosmic Microwave Background anisotropies. By combining the 2dFGRS and CMB data we find the linear-theory rms mass fluctuations in 8 Mpc/h spheres to be sigma_8 = 0.73 +-0.05 (after marginalization over the matter density parameter Omega_m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scale-independent bias parameter of present-epoch L_s = 1.9L_* APM-selected galaxies to be b(L_s,z=0) = 1.10 +- 0.08 on comoving scales of 0.02 < k < 0.15 h/Mpc. If luminosity segregation operates on these scales, L_* galaxies would be almost un-biased, b(L_*,z=0) = 0.96. These results are derived by assuming a flat Lambda-CDM Universe, and by marginalizing over other free parameters and fixing the spectral index n=1 and the optical depth due to reionization tau=0. We also study the best fit pair (Omega_m,b), and the robustness of the results to varying n and tau. Various modelling corrections can each change the resulting b by 5-15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the SDSS, cluster abundance and cosmic shear., Comment: corrected result for the biasing parameter and minor changes to match the MNRAS accepted version

The 2dF Galaxy Redshift Survey (2dFGRS) has already measured over 200,000 redshifts of nearby (median redshift z~0.1) galaxies. This is the single largest set of galaxy spectra ever collected. It allows us to subdivide the survey into subsets according to the galaxy intrinsic properties. We outline here a method (based on Principal Component Analysis) for spectrally classifying these galaxies in a robust and independent manner. In so doing we develop a continuous measure of spectral type, eta, which reflects the actual distribution of spectra in the observed galaxy population. We demonstrate the usefulness of this classification by estimating luminosity functions and clustering per spectral type., Comment: 7 pages, to appear in `Where's the Matter? Tracing Dark and Bright Matter with the New Generation of Large Scale Surveys', June 2001, Treyer & Tresse Eds, Frontier Group

The 2 degree Field (2dF) galaxy redshift survey will involve obtaining approximately 2.5 x 10^5 spectra of objects previously identified as galaxy candidates on morphological grounds. Included in these spectra should be about ten gravitationally-lensed quasars, all with low-redshift galaxies as deflectors (as the more common lenses with high-redshift deflectors will be rejected from the survey as multiple point-sources). The lenses will appear as superpositions of galaxy and quasar spectra, and both cross-correlation techniques and principal components analysis should be able to identify candidates systematically. With the 2dF survey approximately half-completed it is now viable to begin a systematic search for these spectroscopic lenses, and the first steps of this project are described here., Comment: PASA (OzLens edition), in press; 4 pages, 0 figures

We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey and by the latest measurements of the Cosmic Microwave Background anisotropies. By combining the 2dFGRS and CMB data we find the linear-theory rms mass fluctuations in 8 Mpc/h spheres to be sigma_8 = 0.73 +-0.05 (after marginalization over the matter density parameter Omega_m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scale-independent bias parameter of present-epoch L_s = 1.9L_* APM-selected galaxies to be b(L_s,z=0) = 1.10 +- 0.08 on comoving scales of 0.02 < k < 0.15 h/Mpc. If luminosity segregation operates on these scales, L_* galaxies would be almost un-biased, b(L_*,z=0) = 0.96. These results are derived by assuming a flat Lambda-CDM Universe, and by marginalizing over other free parameters and fixing the spectral index n=1 and the optical depth due to reionization tau=0. We also study the best fit pair (Omega_m,b), and the robustness of the results to varying n and tau. Various modelling corrections can each change the resulting b by 5-15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the SDSS, cluster abundance and cosmic shear., Comment: corrected result for the biasing parameter and minor changes to match the MNRAS accepted version

The 2dF Galaxy Redshift Survey (2dFGRS) has already measured over 200,000 redshifts of nearby (median redshift z~0.1) galaxies. This is the single largest set of galaxy spectra ever collected. It allows us to subdivide the survey into subsets according to the galaxy intrinsic properties. We outline here a method (based on Principal Component Analysis) for spectrally classifying these galaxies in a robust and independent manner. In so doing we develop a continuous measure of spectral type, eta, which reflects the actual distribution of spectra in the observed galaxy population. We demonstrate the usefulness of this classification by estimating luminosity functions and clustering per spectral type., Comment: 7 pages, to appear in `Where's the Matter? Tracing Dark and Bright Matter with the New Generation of Large Scale Surveys', June 2001, Treyer & Tresse Eds, Frontier Group

The 2 degree Field (2dF) galaxy redshift survey will involve obtaining approximately 2.5 x 10^5 spectra of objects previously identified as galaxy candidates on morphological grounds. Included in these spectra should be about ten gravitationally-lensed quasars, all with low-redshift galaxies as deflectors (as the more common lenses with high-redshift deflectors will be rejected from the survey as multiple point-sources). The lenses will appear as superpositions of galaxy and quasar spectra, and both cross-correlation techniques and principal components analysis should be able to identify candidates systematically. With the 2dF survey approximately half-completed it is now viable to begin a systematic search for these spectroscopic lenses, and the first steps of this project are described here., Comment: PASA (OzLens edition), in press; 4 pages, 0 figures

High signal-to-noise integrated spectra of the metal-rich globular cluster 47 Tuc, spanning the H-gamma(HR) and Fe4668 line indices, have been obtained. The combination of these indices has been suggested (Jones & Worthey 1995, ApJ, 446, L31) as the best available mechanism for cleanly separating the age-metallicity degeneracy which hampers the dating of distant, unresolved, elliptical galaxies. For the first time, we apply this technique to a nearby spheroidal system, 47 Tuc, for which independent ages, based upon more established methods, exist. Such an independent test of the technique's suitability has not been attempted before, but is an essential one before its application to more distant, unresolved, stellar populations can be considered valid. Because of its weak series of Balmer lines, relative to model spectra, our results imply a spectroscopic ``age'' for 47 Tuc well in excess of 20 Gyr, at odds with the colour-magnitude diagram age of 14+/-1 Gyr. The derived metal abundance, however, is consistent with the known value. Emission ``fill-in'' of the H-gamma line as the source of the discrepancy cannot be entirely excluded by existing data, although the observational constraints are restrictive., Comment: 17 pages, 4 figures, LaTeX, accepted for publication in The Astronomical Journal, also available at http://casa.colorado.edu/~bgibson/publications.html

We present a detailed analysis of the two-point correlation function, ξ(σ, π), from the 2dF Galaxy Redshift Survey (2dFGRS). The large size of the catalogue, which contains ∼220 000 redshifts, allows us to make high-precision measurements of various properties of the galaxy clustering pattern. The effective redshift at which our estimates are made is zs≈ 0.15, and similarly the effective luminosity, Ls≈ 1.4L*. We estimate the redshift-space correlation function, ξ(s), from which we measure the redshift-space clustering length, s0= 6.82 ± 0.28 h−1 Mpc. We also estimate the projected correlation function, Ξ(σ), and the real-space correlation function, ξ(r), which can be fit by a power law (r/r0), with r0= 5.05 ± 0.26 h−1 Mpc, γr= 1.67 ± 0.03. For r≳ 20 h−1 Mpc, ξ drops below a power law as, for instance, is expected in the popular Λ cold dark matter model. The ratio of amplitudes of the real- and redshift-space correlation functions on scales of 8-30 h−1 Mpc gives an estimate of the redshift-space distortion parameter β. The quadrupole moment of ξ(σ, π) on scales 30-40 h−1 Mpc provides another estimate of β. We also estimate the distribution function of pairwise peculiar velocities, ƒ(v), including rigorously the significant effect due to the infall velocities, and we find that the distribution is well fit by an exponential form. The accuracy of our ξ(σ, π) measurement is sufficient to constrain a model, which simultaneously fits the shape and amplitude of ξ(r) and the two redshift-space distortion effects parametrized by β and velocity dispersion, a. We find β= 0.49 ± 0.09 and a= 506 ± 52 km s−1, although the best-fitting values are strongly correlated. We measure the variation of the peculiar velocity dispersion with projected separation, a(σ), and find that the shape is consistent with models and simulations. This is the first time that β and ƒ(v) have been estimated from a self-consistent model of galaxy velocities. Using the constraints on bias from recent estima

We have calculated the two-point correlation functions in redshift space, ξ(σ, π), for galaxies of different spectral types in the 2dF Galaxy Redshift Survey. Using these correlation functions, we are able to estimate values of the linear redshift-space distortion parameter, β≡Ω0.6m/b, the pairwise velocity dispersion, a, and the real-space correlation function, ξ(r), for galaxies with both relatively low star formation rates (for which the present rate of star formation is less than 10 per cent of its past averaged value) and galaxies with higher current star formation activity. At small separations, the real-space clustering of passive galaxies is very much stronger than that of the more actively star-forming galaxies; the correlation-function slopes are, respectively, 1.93 and 1.50, and the relative bias between the two classes is a declining function of scale. On scales larger than 10 h−1 Mpc, there is evidence that the relative bias tends to a constant, bpassive/bactive≃ 1. This result is consistent with the similar degrees of redshift-space distortions seen in the correlation functions of the two classes - the contours of ξ(σ, π) require βactive= 0.49 ± 0.13 and βpassive= 0.48 ± 0.14. The pairwise velocity dispersion is highly correlated with β. Despite this, a significant difference is seen between the two classes. Over the range 8-20 h−1 Mpc, the pairwise velocity dispersion has mean values of 416 ± 76 and 612 ± 92 km s−1 for the active and passive galaxy samples, respectively. This is consistent with the expectation from morphological segregation, in which passively evolving galaxies preferentially inhabit the cores of high-mass virialized regions

We present an analysis of the relative bias between early- and late-type galaxies in the Two-degree Field Galaxy Redshift Survey (2dFGRS) - as defined by the η parameter of Madgwick et al., which quantifies the spectral type of galaxies in the survey. We calculate counts in cells for flux-limited samples of early- and late-type galaxies, using approximately cubical cells with sides ranging from 7 to 42 h−1 Mpc. We measure the variance of the counts in cells using the method of Efstathiou et al., which we find requires a correction for a finite volume effect equivalent to the integral constraint bias of the autocorrelation function. Using a maximum-likelihood technique we fit lognormal models to the one-point density distribution, and develop methods of dealing with biases in the recovered variances resulting from this technique. We then examine the joint density distribution function, f(δE, δL), and directly fit deterministic bias models to the joint counts in cells. We measure a linear relative bias of ≈1.3, which does not vary significantly with ℓ. A deterministic linear bias model is, however, a poor approximation to the data, especially on small scales (ℓ≤ 28h−1 Mpc) where deterministic linear bias is excluded at high significance. A power-law bias model with index b1≈ 0.75 is a significantly better fit to the data on all scales, although linear bias becomes consistent with the data for ℓ≳ 40h−1 Mpc