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Jean M. Quashnock

Publications and source records attributed to Jean M. Quashnock.

17 recordsLinked to original sources
arXiv2009

A Cross-Correlation Analysis of Mg II Absorption Line Systems and Luminous Red Galaxies from the SDSS DR5

We analyze the cross-correlation of 2,705 unambiguously intervening Mg II (2796,2803A) quasar absorption line systems with 1,495,604 luminous red galaxies (LRGs) from the Fifth Data Release of the Sloan Digital Sky Survey within the redshift range 0.36<=z<=0.8. We confirm with high precision a previously reported weak anti-correlation of equivalent width and dark matter halo mass, measuring the average masses to be log M_h(M_[solar]h^-1)=11.29 [+0.36,-0.62] and log M_h(M_[solar]h^-1)=12.70 [+0.53,-1.16] for systems with W[2796A]>=1.4A and 0.8A<=W[2796A]<1.4A, respectively. Additionally, we investigate the significance of a number of potential sources of bias inherent in absorber-LRG cross-correlation measurements, including absorber velocity distributions and the weak lensing of background quasars, which we determine is capable of producing a 20-30% bias in angular cross-correlation measurements on scales less than 2'. We measure the Mg II - LRG cross-correlation for 719 absorption systems with v<60,000 km s^-1 in the quasar rest frame and find that these associated absorbers typically reside in dark matter haloes that are ~10-100 times more massive than those hosting unambiguously intervening Mg II absorbers. Furthermore, we find evidence for evolution of the redshift number density, dN/dz, with 2-sigma significance for the strongest (W>2.0A) absorbers in the DR5 sample. This width-dependent dN/dz evolution does not significantly affect the recovered equivalent width-halo mass anti-correlation and adds to existing evidence that the strongest Mg II absorption systems are correlated with an evolving population of field galaxies at z<0.8, while the non-evolving dN/dz of the weakest absorbers more closely resembles that of the LRG population.

astro-ph.CO↗
arXiv2000

A Measurement of the Three-Dimensional Clustering of C IV Absorption-Line Systems on Scales of 5 to 300 Mpc

We examine the three-dimensional clustering of C IV absorption-line systems, using an extensive catalog of QSO heavy-element absorbers drawn from the literature. We measure clustering by a volume-weighted integral of the correlation function called the reduced second-moment measure, and include information from both along and across QSO lines of sight, thus enabling a full determination of the three-dimensional clustering of absorbers, as well as a comparison of line- and cross-line-of-sight clustering properties. Here we present the three-dimensional reduced second-moment estimator for a three-dimensional point process probed by one-dimensional lines of sight, and apply our algorithm to a sample of 345 C IV absorbers with median redshift of 2.2, drawn from the spectra of 276 QSOs. We confirm the existence of significant clustering on comoving scales up to 100 Mpc, and find that the additional cross-line-of-sight information strengthens the evidence for clustering on scales from 100 Mpc to 150 Mpc. There is no evidence of absorber clustering along or across lines of sight for scales from 150 Mpc to 300 Mpc. We show that with a 300-times larger catalog, such as that to be compiled by the Sloan Digital Sky Survey (100,000 QSOs), use of the full three-dimensional estimator and cross-line-of-sight information will substantially increase clustering sensitivity. We find that standard errors are reduced by an additional factor of 2 to 20 on scales of 30 to 200 Mpc, effectively increasing the sample size by an extra factor of 4 to 400 at large distances.

astro-ph↗
arXiv2000

Estimating the K-function of a point process with an application to cosmology

Motivated by the study of an important data set for understanding the large-scale structure of the universe, this work considers the estimation of the reduced second moment function, or K-function, of a stationary point process observed over a large number of segments of possibly varying lengths. Theory and simulation are used to compare the behavior of isotropic and rigid motion correction estimators and some modifications of these estimators. These results generally support the use of modified versions of the rigid motion correction. When applied to a catalog of astronomical objects known as absorbers, the proposed methods confirm results from earlier analyses of the absorber catalog showing clear evidence of clustering up to 50 Mpc and marginal evidence for clustering of matter on spatial scales beyond 100 Mpc, which is beyond the distance at which clustering of matter is now generally accepted to exist.

physics.data-an↗
arXiv1999

Cluster-Cluster Strong Lensing: Expectations and Detection Methods

We calculate the all-sky number of galaxy clusters that are expected to be gravitationally lensed by foreground massive clusters. We describe the redshift and number distributions of clusters using a Press-Schechter analysis, and model the foreground lensing clusters as singular isothermal spheres. If Omega_m=0.3 and Omega_Lambda=0.7, we expect ~ 30 cluster-cluster strong lensing events that involve foreground X-ray luminous clusters with total mass greater than 7.5 x 10^14 h^-1 M_sun, or X-ray luminosity L_x (2-10 keV) 8 x 10^44 h^-2 ergs s^-1, and background clusters with total mass greater than 10^14 h^-1 M_sun. The number expected in an open universe with Omega_m = 0.3 is less than \~ 4. Because of uncertainty in sigma_8, the root-mean-square density fluctuations in spheres of radius 8 h^-1 Mpc, the exact number of such lensing events is uncertain by a factor of about 5. We examine methods to detect cluster-cluster lensing events based on optical, X-ray, and Sunyaev-Zel'dovich effect observations.

astro-ph↗
arXiv1999

Optical and Near Infrared Observations of the Afterglow of GRB 980329 from 15 Hours to 10 Days

We report I-band observations of the GRB 980329 field made on March 29 with the 1.34-m Tautenberg Schmidt telescope, R-, J- and K-band observations made on April 1 with the APO 3.5-m telescope, R- and I-band observations made on April 3 with the Mayall 4-m telescope at KPNO, and J- and K-band observations made between April 6 - 8 with the Keck-I 10-m telescope. We show that these and other reported measurements are consistent with a power-law fading of the optical/near infrared source that is coincident with the variable radio source VLA J0702+3850. This firmly establishes that this source is the afterglow of GRB 980329.

astro-ph↗
arXiv1998

A Lower Limit on Omega-Lambda Using Gravitational Lensing in the Hubble Deep Field

We calculate the expected number of multiply-imaged galaxies in the Hubble Deep Field (HDF), using photometric redshift information for galaxies with $m_I < 27$ that were detected in all four HDF passbands. A comparison of these expectations with the observed number of strongly lensed galaxies places a lower limit on the current value of $Ω_m-Ω_Λ$, where $Ω_m$ is the cosmological mass density of the universe and $Ω_Λ$ is the normalized cosmological constant. Based on current estimates of the HDF luminosity function and associated uncertainties in individual parameters, our 95% confidence lower limit on $Ω_m-Ω_Λ$ is between -0.44, if there are no strongly lensed galaxies in the HDF, and -0.73, if there are two strongly lensed galaxies in the HDF. If the only lensed galaxy in the HDF is the one presently viable candidate, then, in a flat universe ($Ω_m+Ω_Λ=1$), $Ω_Λ < 0.79$ (95% C.L.). These lower limits are compatible with estimates based on high-redshift supernovae and with previous limits based on gravitational lensing.

astro-ph↗
arXiv1998

A New Measure of the Clustering of QSO Heavy-Element Absorption-Line Systems

We examine the line-of-sight clustering of QSO heavy-element absorption-line systems, using a new measure of clustering, called the reduced second moment measure, that directly measures the mean over-density of absorbers. While closely related to other second-order measures such as the correlation function or the power spectrum, this measure has a number of distinct statistical properties which make possible a continuous exploration of clustering as a function of scale. From a sample of 352 C IV absorbers with median redshift 2.2, drawn from the spectra of 274 QSOs, we find that the absorbers are strongly clustered on scales from 1 to 20 Mpc. Furthermore, there appears to be a sharp break at 20 Mpc, with significant clustering on scales up to 100 Mpc in excess of that which would be expected from a smooth transition to homogeneity. There is no evidence of clustering on scales greater than 100 Mpc. These results suggest that strong C IV absorbers along a line of sight are indicators of clusters and possibly superclusters, a relationship that is supported by recent observations of ``Lyman break'' galaxies.

astro-ph↗
arXiv1998

Gravitational Lensing and the Hubble Deep Field

We calculate the expected number of multiply-imaged galaxies in the Hubble Deep Field (HDF), using photometric redshift information for galaxies with m_I < 27 that were detected in all four HDF passbands. A comparison of these expectations with the observed number of strongly lensed galaxies constrains the current value of Omega_m-Omega_Lambda, where Omega_m is the mean mass density of the universe and Omega_Lambda is the normalized cosmological constant. Based on current estimates of the HDF luminosity function and associated uncertainties in individual parameters, our 95% confidence lower limit on Omega_m-Omega_Lambda ranges between -0.44, if there are no strongly lensed galaxies in the HDF, and -0.73, if there are two strongly lensed galaxies in the HDF. If the only lensed galaxy in the HDF is the one presently viable candidate, then, in a flat universe (Omega_m+Omega_Lambda=1), Omega_Lambda < 0.79 (95% C.L.). These limits are compatible with estimates based on high-redshift supernovae and with previous limits based on gravitational lensing.

astro-ph↗
arXiv1998

Gravitational Lensing Limits on the Average Redshift of Gamma-Ray Bursts

The lack of bright host galaxies in several recently examined gamma-ray burst (GRB) error boxes suggests that the redshifts of cosmological GRBs may be significantly higher than previously believed. On the other hand, the non-detection of multiple images in the BATSE 4B catalog implies an upper limit on the average redshift of GRBs. Here, we calculate an upper limit to , independent of the physical model for GRBs, using a new statistical lensing method that removes distance ambiguities, and thus permits accurate computation of the lensing rate at high z. The upper limit on depends directly on the cosmological parameters Omega and Lambda. If there are no multiple images among the brightest 80% of the first 1802 bursts in the BATSE 4B catalog, then, at the 95% confidence level, is less than 2.2, 2.8, 4.3, or 5.3 for (Omega,Lambda) values of (0.3, 0.7), (0.5, 0.5), (0.5, 0.0), or (1.0, 0.0), respectively. The 68% upper limit to the average redshift is comparable to or less than the median redshift of GRBs in scenarios in which the GRB rate is proportional to the rate of star formation, for any cosmology. The uncertainty in the lensing rate --- arising from uncertainties in the cosmological parameters and in the number density and average velocity dispersion of galaxies --- will be reduced significantly in the next few years by a new generation of experiments and surveys. Moreover, the continued increase in the number of GRBs observed by BATSE will greatly constrain their redshift distribution.

astro-ph↗
arXiv1998

Are The Four Gamma-Ray Bursts of 1996 October 27-29 Due to Repetition of a Single Source?

BATSE, Ulysses, and TGRS and KONUS on WIND detected four gamma-ray events within 1.8 days during 1996 October 27-29, consistent with coming from the same location on the sky. We assess the evidence that these events may be due to a series of bursts from a single source by calculating the probability that such a clustering in position and in time of occurrence might happen by chance. The calculation of this probability is afflicted by the usual problem of a posteriori statistics. We introduce a clustering statistic, which is formed from the "minimum circle radius" (i.e. the radius of the smallest circle that just encloses the positions of all the events) and the minimum time lapse (i.e. the time elapsed between the first and last event). We also introduce a second clustering statistic, which is formed from the "cluster likelihood function" and the minimum time lapse. We show that the use of these statistics largely eliminates the "a posteriori" nature of the problem. The two statistics yield significances of the clustering of $3.3\times 10^{-4}$ and $3.1\times 10^{-5}$, respectively, if we interpret the four events as four bursts, whereas the clustering is not significant if we interpret the four events as only three bursts. However, in the latter case one of the bursts is the longest ever observed by BATSE.

astro-ph↗
arXiv1998

The Form and Evolution of the Clustering of QSO Heavy-Element Absorption-Line Systems

We have analyzed the clustering of C IV and Mg II absorption-line systems on comoving scales from 1 to 16 \hMpc, using an extensive catalog of heavy-element QSO absorbers with mean redshift 2.2 (C IV) and 0.9 (Mg II). We find that, for the C IV sample as a whole, the absorber line-of-sight correlation function is well-fit by a power law with index $γ= 1.75 ^{+0.50}_{-0.70}$ and comoving correlation length $r_0 = 3.4 ^{+0.7}_{-1.0}$ \hMpc ($q_0=0.5$). The clustering of absorbers at high redshift is thus of a form like that of galaxies and clusters at low redshift, and of amplitude such that absorbers are correlated on scales of galaxy clusters. We also trace the evolution of the mean amplitude $ξ_0(z)$ of the correlation function from $z=3$ to $z=0.9$. We find that, when parametrized as $ξ_0(z)\propto (1+z)^{-(3+ε)+γ}$, the amplitude grows rapidly with decreasing redshift, with maximum-likelihood value for the evolutionary parameter of $ε= 2.05 \pm 1.0$ ($q_0=0.5$). When extrapolated to zero redshift, the correlation length is $r_0 = 30 ^{+22}_{-13}$ \hMpc . This suggests that the strong C IV and Mg II absorbers, on megaparsec scales, are biased tracers of the higher-density regions of space, and that agglomerations of strong absorbers along a line of sight are indicators of clusters and superclusters. This is supported by recent observations of ``Lyman break'' galaxies. The rapid growth seen in the clustering of absorbers mimics that expected in a a critical universe from linear theory of gravitational instability, and is consistent with gravitationally induced growth of perturbations.

astro-ph↗
arXiv1997

The Clustering of C IV and Mg II Absorption-Line Systems

We have analyzed the clustering of C IV and Mg II absorption-line systems on comoving scales from 1 to 16 \hMpc, using an extensive catalog of heavy-element QSO absorbers with mean redshift 2.2 (C IV) and 0.9 (Mg II). For the C IV sample as a whole, the absorber line-of-sight correlation function is well fit by a power law of the form $ξ(r)=(r_0/r)^γ$, with maximum-likelihood values of $γ= 1.75 ^{+0.50}_{-0.70}$ and comoving $r_0 = 3.4 ^{+0.7}_{-1.0}$ \hMpc ($q_0=0.5$). This clustering is of the same form as that for galaxies and clusters at low redshift, and of amplitude such that absorbers are correlated on scales of clusters of galaxies. We also trace the evolution of the mean amplitude $ξ_0(z)$ of the correlation function from $z=3$ to $z=0.9$. We find that, when parametrized as $ξ_0(z)\propto (1+z)^{-(3+ε)+γ}$, the amplitude grows rapidly with decreasing redshift, with maximum-likelihood value for the evolutionary parameter of $ε= 2.05 \pm 1.0$. The rapid growth seen in the clustering of absorbers is consistent with gravitationally induced growth of perturbations.

astro-ph↗
arXiv1996

High-Redshift Superclustering of QSO Absorption Line Systems on 100 Mpc Scales

We have analyzed the clustering of C IV absorption line systems in an extensive new catalog of heavy element QSO absorbers. The catalog permits exploration of clustering over a large range in both scale (from about 1 to over 300 Mpc) and redshift (z from 1.2 to 4.5). We find significant evidence (5.0 sigma) that C IV absorbers are clustered on comoving scales of 100 Mpc and less --- similar to the size of voids and walls found in galaxy redshift surveys of the local universe --- with a mean correlation function $ξ= 0.42 \pm 0.10$ over these scales. We find, on these scales, that the mean correlation function at low (z=1.7), medium (z=2.4), and high redshift (z=3.0) is $ξ=0.40 \pm 0.17$, $0.32 \pm 0.14$, and $0.72 \pm 0.25$, respectively. Thus, the superclustering is present even at high redshift; furthermore, it does not appear that the superclustering scale, in comoving coordinates, has changed significantly since then. We find 7 QSOs with rich groups of absorbers (potential superclusters) that account for a significant portion of the clustering signal, with 2 at redshift $z\sim 2.8$. We find that the superclustering is just as evident if we take $q_0=0.1$ instead of 0.5; however, the inferred scale of clustering is then 240 Mpc , which is larger than the largest scales of clustering known at present. This discrepancy may be indicative of a larger value of $q_0$, and hence $Ω_0$. The evolution of the correlation function on 50 Mpc scales is consistent with that expected in cosmologies with density parameter ranging from $Ω_0 = $ 0.1 to 1. Finally, we find no evidence for clustering on scales greater than 100 Mpc ($q_0=0.5$) or 240 Mpc ($q_0=0.1$).

astro-ph↗
arXiv1996

An Excess of C IV Absorbers in Luminous QSOs: Evidence for Gravitational Lensing?

We have compiled a new and extensive catalog of heavy-element QSO absorption line systems and analyzed the distribution of absorbers in bright and faint QSOs, to search for gravitational lensing of background QSOs by the matter associated with the absorbers. There is a highly significant excess of C {\sc iv} absorbers in bright QSOs in the redshift range $z=1.2-3.2$, and this excess increases strongly as a function of QSO absolute magnitude. No significant excess is found for Mg {\sc ii} absorbers in the redshift range $z=0.30-1.55$. We rule out several possible reasons for this effect and argue that the C {\sc iv} excess could be due to gravitational lensing. If so, then the lensing masses must be at $z \gtrsim 1.5$ and within several hundred comoving Mpc of the QSOs, where the C {\sc iv} absorbers are mainly found. The absence of an excess in the available Mg {\sc ii} sample would then arise because the Mg {\sc ii} data does not sample this region of space.

astro-ph↗
arXiv1996

A Constraint on the Distance Scale to Cosmological Gamma--Ray Bursts

If \g--ray bursts are cosmological in origin, the sources are expected to trace the large--scale structure of luminous matter in the universe. I use a new likelihood method that compares the counts--in--cells distribution of \g--ray bursts in the BATSE 3B catalog with that expected from the known large--scale structure of the universe, in order to place a constraint on the distance scale to cosmological bursts. I find, at the 95\% confidence level, that the comoving distance to the ``edge'' of the burst distribution is greater than $630~h^{-1}$~Mpc ($z > 0.25$), and that the nearest burst is farther than $40~h^{-1}$~Mpc. The median distance to the nearest burst is $170~h^{-1}$~Mpc, implying that the total energy released in \g--rays during a burst event is of order $3\times 10^{51}~h^{-2}$ ergs. None of the bursts that have been observed by BATSE are in nearby galaxies, nor is a signature from the Coma cluster or the ``Great Wall'' likely to be seen in the data at present.

astro-ph↗
arXiv1995

A Constraint on the Distance Scale to Cosmological Gamma--Ray Bursts

If gamma-ray bursts have a cosmological origin, the sources are expected to trace the large-scale structure of luminous matter in the universe. I use a new likelihood method that compares the counts-in-cells distribution of gamma-ray bursts in the BATSE 3B catalog with that expected from the known large-scale structure of the universe, in order to place a constraint on the distance scale to cosmological bursts. I find, at the 95% confidence level, that the comoving distance to the ``edge'' of the burst distribution is greater than 630 $h^{-1}$ Mpc (z > 0.25), and that the nearest burst is farther than 40 $h^{-1}$ Mpc. The median distance to the nearest burst is 170 $h^{-1}$ Mpc, implying that the total energy released in gamma-rays during a burst event is of order $3 \times 10^{51}~h^{-2}$ erg. None of the bursts that have been observed by BATSE are in nearby galaxies, nor is a signature from the Coma cluster or the ``Great Wall'' likely to be seen in the data at present.

astro-ph↗
arXiv1995

Likelihood Analysis of Repeating in the BATSE Catalogue

I describe a new likelihood technique, based on counts-in-cells statistics, that I use to analyze repeating in the BATSE 1B and 2B catalogues. Using the 1B data, I find that repeating is preferred over non-repeating by 4.3:1 odds, with a well-defined peak at 5-6 repetitions per source. I find that the post-1B data are consistent with the repeating model inferred from the 1B data, after taking into account the lower fraction of bursts with well-determined positions. Combining the two data sets, I find that the odds favoring repeating over non-repeating are almost unaffected at 4:1, with a narrower peak at 5 repetitions per source. I conclude that the data sets are consistent both with each other and with repeating, and that for these data sets the odds favor repeating.

astro-ph↗