arXiv subjects

Daniel H. McIntosh

Publications and source records attributed to Daniel H. McIntosh.

At least 73 records · Page 4Linked to original sources

arXiv2006

Color, Structure, and Star Formation History of Dwarf Galaxies over the last ~3 Gyr with GEMS and SDSS

We present a study of the colors, structural properties, and star formation histories for a sample of ~1600 dwarfs over look-back times of ~3 Gyr (z=0.002-0.25). The sample consists of 401 distant dwarfs drawn from the Galaxy Evolution from Morphologies and SEDs (GEMS) survey, which provides high resolution Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) images and accurate redshifts, and of 1291 dwarfs at 10-90 Mpc compiled from the Sloan Digitized Sky Survey (SDSS). The sample is complete down to an effective surface brightness of 22 mag arcsec^-2 in z and includes dwarfs with M_g=-18.5 to -14 mag. Rest-frame luminosities in Johnson UBV and SDSS ugr filters are provided by the COMBO-17 survey and structural parameters have been determined by Sérsic fits. We find that the GEMS dwarfs are bluer than the SDSS dwarfs by ~0.13 mag in g-r, which is consistent with the color evolution over ~2 Gyr of star formation histories involving moderate starbursts and long periods of continuous star formation. The full color range of the samples cannot be reproduced by single starbursts of different masses or long periods of continuous star formation alone. Furthermore, an estimate of the mechanical luminosities needed for the gas in the GEMS dwarfs to be completely removed from the galaxies shows that a significant number of low luminosity dwarfs are susceptible to such a complete gas loss, if they would experience a starburst. On the other hand, a large fraction of more luminous dwarfs is likely to retain their gas. We also estimate the star formation rates per unit area for the GEMS dwarfs and find good agreement with the values for local dwarfs.

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arXiv2005

Studying distant dwarf galaxies with GEMS and SDSS

We study the colors, structural properties, and star formation histories of a sample of ~1600 dwarfs over look-back times of ~3 Gyr (z=0.002-0.25). The sample consists of 401 distant dwarfs drawn from the Galaxy Evolution from Morphologies and SEDs (GEMS) survey, which provides high resolution Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) images and accurate redshifts, and of 1291 dwarfs at 10-90 Mpc compiled from the Sloan Digitized Sky Survey (SDSS). We find that the GEMS dwarfs are bluer than the SDSS dwarfs, which is consistent with star formation histories involving starbursts and periods of continuous star formation. The full range of colors cannot be reproduced by single starbursts or constant star formation alone. We derive the star formation rates of the GEMS dwarfs and estimate the mechanical luminosities needed for a complete removal of their gas. We find that a large fraction of luminous dwarfs are likely to retain their gas, whereas fainter dwarfs are susceptible to a significant gas loss, if they would experience a starburst.

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arXiv2005

Nature and completeness of galaxies detected in the Two Micron All Sky Survey

We cross correlate the well-defined and very complete spectroscopic Main Galaxy Sample (MGS) of 156,000 bright (r<17.5 mag) galaxies from the SDSS with 2MASS sources to explore the nature and completeness of the 2MASS K-band selection of nearby galaxies. 2MASS detects 90% of the MGS brighter than r=17 mag. For r<16, 93.1% of the MGS is found in the 2MASS Extended Source Catalog (XSC). These detections span the representative range of optical and near-IR galaxy properties, but with a surface brightness-dependent bias to preferentially miss the most blue and low-concentration sources, consistent with the most morphologically late-type galaxy population. An XSC completeness of 97.5% is achievable at bright magnitudes, with blue LSBs being the only major source of incompleteness, if one follows our careful matching criteria and weeds out spurious SDSS sources. We conclude that the rapid drop in XSC completeness at r>16 reflects the sharp surface-brightness limit of the extended source detection algorithm in 2MASS. As a result, the r>16 galaxies found in the XSC are over-representative in red early types and under-representative in blue latetypes. At r>16 the XSC suffers an additional selection effect from the 2-3" spatial resolution limit of 2MASS. Therefore, 2MASS continues to detect 90% of of the MGS at 16<r<17, but with a growing fraction found in the Point Source Catalog (PSC) only. Overall, one third of the MGS is detected in the 2MASS PSC but not the XSC. A combined K<13.57 and r<16 selection provides the most representative inventory of galaxies in the local cosmos with near-IR and optical measurements, and 90.8% completeness. Using data from SDSS-DR2, this sample contains 19,156 galaxies with a median redshift of 0.052. (abridged)

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arXiv2005

Dry Mergers in GEMS: The Dynamical Evolution of Massive Early-Type Galaxies

We have used the 28'x 28' HST image mosaic from the GEMS (Galaxy Evolution from Morphology and SEDs) survey in conjunction with the COMBO-17 photometric redshift survey to constrain the incidence of major mergers between spheroid-dominated galaxies with little cold gas (dry mergers) since z = 0.7. A set of N-body merger simulations was used to explore the morphological signatures of such interactions: they are recognizable either as < 5kpc separation close pairs or because of broad, low surface brightness tidal features and asymmetries. Data with the depth and resolution of GEMS are sensitive to dry mergers between galaxies with M_V < -20.5 for z < 0.7; dry mergers at higher redshifts are not easily recovered in single-orbit HST imaging. Six dry mergers (12 galaxies) with luminosity ratios between 1:1 and 4:1 were found from a sample of 379 red early-type galaxies with M_V < -20.5 and 0.1 < z < 0.7. The simulations suggest that the morphological signatures of dry merging are visible for ~250Myr and we use this timescale to convert the observed merger incidence into a rate. On this basis we find that present day spheroidal galaxies with M_V < -20.5 on average have undergone between 0.5 and 2 major dry mergers since z ~ 0.7. We have compared this result with the predictions of a Cold Dark Matter based semi-analytic galaxy formation model. The model reproduces the observed declining major merger fraction of bright galaxies and the space density of luminous early-type galaxies reasonably well. The predicted dry merger fraction is consistent with our observational result. Hence, hierarchical models predict and observations now show that major dry mergers are an important driver of the evolution of massive early-type galaxies in recent epochs.

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arXiv2005

Cosmological weak lensing with the HST GEMS survey

We present our cosmic shear analysis of GEMS, one of the largest wide-field surveys ever undertaken by the Hubble Space Telescope. Imaged with the Advanced Camera for Surveys (ACS), GEMS spans 795 square arcmin in the Chandra Deep Field South. We detect weak lensing by large-scale structure in high resolution F606W GEMS data from ~60 resolved galaxies per square arcminute. We measure the two-point shear correlation function, the top-hat shear variance and the shear power spectrum, performing an E/B mode decomposition for each statistic. We show that we are not limited by systematic errors and use our results to place joint constraints on the matter density parameter Omega_m and the amplitude of the matter power spectrum sigma_8. We find sigma_8(Omega_m/0.3)^{0.65}=0.68 +/- 0.13 where the 1sigma error includes both our uncertainty on the median redshift of the survey and sampling variance. Removing image and point spread function (PSF) distortions are crucial to all weak lensing analyses. We therefore include a thorough discussion on the degree of ACS PSF distortion and anisotropy which we characterise directly from GEMS data. Consecutively imaged over 20 days, GEMS data also allows us to investigate PSF instability over time. We find that, even in the relatively short GEMS observing period, the ACS PSF ellipticity varies at the level of a few percent which we account for with a semi-time dependent PSF model. Our correction for the temporal and spatial variability of the PSF is shown to be successful through a series of diagnostic tests.

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arXiv2005

GEMS: The Size Evolution of Disk Galaxies

We combine HST imaging from the GEMS survey with photometric redshifts from COMBO-17 to explore the evolution of disk-dominated galaxies since z<1.1. The sample is comprised of all GEMS galaxies with Sersic indices n<2.5, derived from fits to the galaxy images. We account fully for selection effects through careful analysis of image simulations; we are limited by the depth of the redshift and HST data to the study of galaxies with absolute magnitudes M(V)<-20, or equivalently stellar masses log(M)>10. We find strong evolution in the magnitude-size scaling relation for galaxies with M(V)<-20, corresponding to a brightening of 1 mag per sqarcsec in rest-frame V-band by z=1. Yet, disks at a given absolute magnitude are bluer and have lower stellar mass-to-light ratios at z=1 than at the present day. As a result, our findings indicate weak or no evolution in the relation between stellar mass and effective disk size for galaxies with log(M)>10 over the same time interval. This is strongly inconsistent with the most naive theoretical expectation, in which disk size scales in proportion to the halo virial radius, which would predict that disks are a factor of two denser at fixed mass at z=1. The lack of evolution in the stellar mass-size relation is consistent with an ``inside-out'' growth of galaxy disks on average (galaxies increasing in size as they grow more massive), although we cannot rule out more complex evolutionary scenarios.

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arXiv2005

Towards an understanding of the rapid decline of the cosmic star formation rate

We present a first analysis of deep 24 micron observations with the Spitzer Space Telescope of a sample of nearly 1500 galaxies in a thin redshift slice, 0.65 2x10^10 solar masses) are undergoing a period of intense star formation above their past-averaged SFR. In contrast, less than 1% of equally-massive galaxies in the local universe have similarly intense star formation activity. Morphologically-undisturbed galaxies dominate the total infrared luminosity density and SFR density: at z~0.7, more than half of the intensely star-forming galaxies have spiral morphologies, whereas less than \~30% are strongly interacting. Thus, a decline in major-merger rate is not the underlying cause of the rapid decline in cosmic SFR since z~0.7. Physical properties that do not strongly affect galaxy morphology - for example, gas consumption and weak interactions with small satellite galaxies - appear to be responsible.

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arXiv2004

The Galaxy Angular Correlation Functions and Power Spectrum from the Two Micron All Sky Survey

We calculate the angular correlation function of galaxies in the Two Micron All Sky Survey. We minimize the possible contamination by stars, dust, seeing and sky brightness by studying their cross correlation with galaxy density, and limiting the galaxy sample accordingly. We measure the correlation function at scales between 1-18 arcdegs using a half million galaxies. We find a best fit power law to the correlation function has a slope of 0.76 and an amplitude of 0.11. However, there are statistically significant oscillations around this power law. The largest oscillation occurs at about 0.8 degrees, corresponding to 2.8 h^{-1} Mpc at the median redshift of our survey, as expected in halo occupation distribution descriptions of galaxy clustering. We invert the angular correlation function using Singular Value Decomposition to measure the three-dimensional power spectrum and find that it too is in good agreement with previous measurements. A dip seen in the power spectrum at small wavenumber k is statistically consistent with CDM-type power spectra. A fit of CDM-type power spectra to k < 0.2 h Mpc^{-1} give constraints of Γ_{eff}=0.116 and σ_8=0.96. This suggest a K_s-band linear bias of 1.1+/-0.2. This Γ_{eff} is different from the WMAP CMB derived value. On small scales the power-law shape of our power spectrum is shallower than that derived for the SDSS. These facts together imply a biasing of these different galaxies that might be nonlinear, that might be either waveband or luminosity dependent, and that might have a nonlocal origin.

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arXiv2004

The Evolution of Early-type Red Galaxies with the GEMS Survey: Luminosity-size and Stellar Mass-size Relations Since z=1

We combine HST/ACS imaging from the GEMS survey with redshifts and rest-frame quantities from COMBO-17 to study the evolution of morphologically early-type galaxies with red colors since z=1. We use a new large sample of 728 galaxies with centrally-concentrated radial profiles (Sersic n>2.5) and rest-frame U-V colors on the red sequence. By appropriate comparison with the local relations from SDSS, we find that the luminosity-size (L-R) and stellar mass-size (M-R) relations evolve in a manner that is consistent with the passive aging of ancient stars. By itself, this result is consistent with a completely passive evolution of the red early-type galaxy population. If instead, as demonstrated by a number of recent surveys, the early-type galaxy population builds up in mass by a factor of 2 since z=1, our results imply that new additions to the early-type galaxy population follow similar L-R and M-R correlations, compared to the older subset of early-type galaxies. Adding early-type galaxies to the red sequence through disk fading appears to be consistent with the data. Through comparison with models, the role of dissipationless merging is limited to <1 major merger on average since z=1 for the most massive galaxies. Predictions from models of gas-rich mergers are not yet mature enough to allow a detailed comparison to our observations. We find tentative evidence that the amount of luminosity evolution depends on galaxy stellar mass, such that the least massive galaxies show stronger luminosity evolution compared to more massive early types. This could reflect a different origin of low-mass early-type galaxies and/or younger stellar populations; the present data is insufficient to discriminate between these possibilities. (abridged)

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arXiv2004

Testing the Universality of the (U-V) Color-Magnitude Relations for Nearby Clusters of Galaxies

We present a detailed U-V CMR analysis for 3 local (z<0.06) Abell (A85, A496, A754) galaxy clusters, with 637 total spectroscopic members down to 0.1L^star. We find that these clusters have similar CMRs with a mean color of U-V=1.4 at M_V=-20+5logh, and narrow limits of intrinsic color scatter [0.047,0.079] and slope [-0.094,-0.075]. The core cluster population of red galaxies follow CMRs that are in close agreement with that of Coma. We test how sensitive the CMR uniformity is to variations in color aperture size and sample selection, and find slightly wider limits of scatter [0.047,0.112] and slope [-0.104,-0.054]. This upper limit for U-V scatter is consistent with z_form>1.2 for the bulk of the stars in red cluster galaxies, and a maximum age spread of 5.2 Gyr. We note that none of the slopes exhibit a break as claimed by Metcalf et al., and using colors from equal-light apertures does not remove the CMR slope. Our findings expand the single Coma data point and provide a much-needed z=0 base-line for comparisons to high-z cluster U-V CMRs. The CMR scatter range in low-z clusters is consistent with that found in high-z clusters, suggesting little evolution in the stars of red cluster galaxies out to z~1. To identify the most recently accreted galaxies, we divide each cluster's membership into 3 galaxy populations based on CMR-relative U-V color. Blue galaxies make up 18-23% of each cluster's galaxy counts above 0.1L^star. We test the hypothesis that CMR-relative color represents rough cluster infall times and find that blue galaxies are spatially, kinematically, and morphologically distinct from red cluster members. These distinctions provide further evidence that bluer members are indeed more recently accreted field spirals as expected in an hierarchical universe. (abridged)

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arXiv2004

The U-band Galaxy Luminosity Function of Nearby Clusters

Despite the great potential of the U-band galaxy luminosity function (GLF) to constrain the history of star formation in clusters, to clarify the question of variations of the GLF across filter bands, to provide a baseline for comparisons to high-redshift studies of the cluster GLF, and to estimate the contribution of bound systems of galaxies to the extragalactic near-UV background, determinations have so far been hampered by the generally low efficiency of detectors in the U-band and by the difficulty of constructing both deep and wide surveys. In this paper, we present U-band GLFs of three nearby, rich clusters to a limit of M_U=-17.5 (M*_U+2). Our analysis is based on a combination of separate spectroscopic and R-band and U-band photometric surveys. For this purpose, we have developed a new maximum-likelihood algorithm for calculating the luminosity function that is particularly useful for reconstructing the galaxy distribution function in multi-dimensional spaces (e.g., the number of galaxies as a simultaneous function of luminosity in different filter bands, surface brightness, star formation rate, morphology, etc.), because it requires no prior assumptions as to the shape of the distribution function. The composite luminosity function can be described by a Schechter function with characteristic magnitude M*_U=-19.82+/-0.27 and faint end slope alpha_U=-1.09+/-0.18. The total U-band GLF is slightly steeper than the R-band GLF, indicating that cluster galaxies are bluer at fainter magnitudes. Quiescent galaxies dominate the cumulative U-band flux for M_U<-14. The contribution of galaxies in nearby clusters to the U-band extragalactic background is <1% Gyr^-1 for clusters of masses ~3*10^14 to 2*10^15 M_solar.

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arXiv2004

Structural Evidence for Environment-Driven Transformation of the Blue Galaxies in Local Abell Clusters - A85, A496, and A754

We compare V-band structural properties of cluster and field galaxies, to test whether much of the current cluster membership resulted from the transformation of infalling spirals into red early types. We use 140 galaxies from 3 z<0.6 Abell clusters (A85,A496,A754 - spectroscopic membership) with blue colors, and compare them to 80 field galaxies with similar colors and luminosities. Our previous work (McIntosh et al. 2004, ApJ submitted) shows that the blue galaxies in these local clusters are a recently infalling population that has yet to encounter the dense core. We quantify galaxy internal structure from 2D B/D decompositions using GIM2D. We observe structural differences between blue galaxies in clusters, compared to the field. Most blue cluster members are physically smaller and fainter than their field counterparts. At a matched size and luminosity, recent arrivals are smoother in appearance, yet their total light is as disk-dominated as in normal field spirals. Moreover, 50% of blue cluster galaxies have blue cores or globally blue color profiles, in contrast with field spirals that have typically red color gradients. Without environment dependent evolution outside of cluster cores, we expect blue disk galaxies in clusters and the field to have similar morphologies, sizes, and color gradients. We show conclusively that galaxy properties do reflect the environment in which the galaxy is found. The data show that the transformation of accreted galaxies is not confined to the dense cluster core. The overall properties of bluer cluster galaxies are best explained by environment-driven transformation of accreted field spirals, and our results suggest that the processes that govern color and morphological evolution occur separately. (abridged)

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arXiv2004

Nearly 5000 Distant Early-Type Galaxies in COMBO-17: a Red Sequence and its Evolution since z~1

We present the rest-frame colors and luminosities of ~25000 m_R<24 galaxies in the redshift range 0.2<z<1.1, drawn from 0.78 square degrees of the COMBO-17 survey. We find that the rest-frame color distribution of these galaxies is bimodal at all redshifts out to z~1. This bimodality permits a model-independent definition of red, early-type galaxies and blue, late-type galaxies at any given redshift. The colors of the blue peak become redder towards the present day, and the number density of blue luminous galaxies has dropped strongly since z~1. Focusing on the red galaxies, we find that they populate a color-magnitude relation. Such red sequences have been identified in galaxy cluster environments, but our data show that such a sequence exists over this redshift range even when averaging over all environments. The mean color of the red galaxy sequence evolves with redshift in a way that is consistent with the aging of an ancient stellar population. The rest-frame B-band luminosity density in red galaxies evolves only mildly with redshift in a Lambda-dominated cold dark matter universe. Accounting for the change in stellar mass-to-light ratio implied by the redshift evolution in red galaxy colors, the COMBO-17 data indicate an increase in stellar mass on the red sequence by a factor of two since z~1. The largest source of uncertainty is large-scale structure, implying that considerably larger surveys are necessary to further refine this result. We explore mechanisms that may drive this evolution in the red galaxy population, finding that both galaxy merging and truncation of star formation in some fraction of the blue, star-forming population are required to fully explain the properties of these galaxies.

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arXiv2004

GEMS: Galaxy Evolution from Morphologies and SEDs

GEMS, Galaxy Evolution from Morphologies and SEDs, is a large-area (800 arcmin2) two-color (F606W and F850LP) imaging survey with the Advanced Camera for Surveys on HST. Centered on the Chandra Deep Field South, it covers an area of ~28'x28', or about 120 Hubble Deep Field areas, to a depth of m_AB(F606W)=28.3 (5sigma and m_AB(F850LP)=27.1 (5sigma) for compact sources. In its central ~1/4, GEMS incorporates ACS imaging from the GOODS project. Focusing on the redshift range 0.2<=z<=1.1, GEMS provides morphologies and structural parameters for nearly 10,000 galaxies where redshift estimates, luminosities and SEDs exist from COMBO-17. At the same time, GEMS contains detectable host galaxy images for several hundred faint AGN. This paper provides an overview of the science goals, the experiment design, the data reduction and the science analysis plan for GEMS.

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arXiv2003

GEMS Imaging of Red Sequence Galaxies at z~0.7: Dusty or Old?

We have used the 30'x30' Hubble Space Telescope image mosaic from the Galaxy Evolution from Morphology and SEDs (GEMS) project in conjunction with the COMBO-17 deep photometric redshift survey to define a sample of nearly 1500 galaxies with 0.65 < z < 0.75. With this sample, we can study the distribution of rest-frame V-band morphologies more than 6 Gyr ago, without differential bandpass shifting and surface brightness dimming across this narrow redshift slice. Focusing on red-sequence galaxies at z ~ 0.7, we find that 85% of their combined rest-frame V-band luminosity density comes from visually-classified E/S0/Sa galaxies (at V-band magnitudes brighter than -19.5). Similar results are obtained if automated classifiers are used. This fraction is identical to that found at the present day, and is biased by less than 10% by large scale structure and the morphology-density relation. Under the assumption that peculiar and edge-on disk galaxies are red by virtue of their dust content, we find that less than 13% of the total rest-frame V-band luminosity of the z ~ 0.7 red galaxy population is from dusty galaxies.

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arXiv2003

Scaling Relations of Local Spiral Galaxies.I. Observational Foundations

(Abridged) This paper presents an exploration of two fundamental scaling relations of spiral galaxies, the luminosity-rotation speed (or Tully-Fisher; TF) relation, and the size-luminosity (SL) relation, and the dependences of their scatter, at red and IR bands. We verify that the observed virial relations of disk galaxies are given by Vobs \prop L^0.31 and Rd \prop L^0.33 using distance-redshift surveys of high surface brightness (HSB) and low surface brightness (LSB) non-interacting galaxies. Thus the galaxy surface brightness (SB) is Sigma \prop Rd \prop Vobs \prop Mvir^0.33. We derive the first extensive J-band TF and SL relations using 2MASS data products. The TF residuals are fully independent of SB and other tested observables. TF relations (TFRs) for various morphological types have different zero points, but a common slope, such that early-type (redder) disks rotate faster than later-types (bluer) of the same luminosity. This dependence of the TFR is a direct consequence of the more fundamental dependence on color, which itself is related to the galaxy star formation history. The SL relation scatter is mostly dominated by SB, but color also plays a small role. The TF and SL residuals for HSB and LSB galaxies are weakly correlated, in agreement with the earlier claim by Courteau & Rix (1999). This suggests that spiral disks of all color, brightness, and barredness are, on average, dominated by dark matter even in their inner parts. The observed scaling relations of disk galaxies are likely the result of the simplest scenario of galaxy formation, but their color dependence remains a challenge to hierarchical structure formation models. The scaling relations and their derivatives are contrasted against galaxy formation models in our companion paper.

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arXiv2003

The Optical and Near-Infrared Properties of Galaxies: I. Luminosity and Stellar Mass Functions

We use a large sample of galaxies from the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to calculate galaxy luminosity and stellar mass functions in the local Universe. We estimate k-corrections, evolution corrections, and stellar mass-to-light ratios (M/Ls) by fitting the galaxy colors with simple models. Our optical and near-infrared luminosity functions agree with most recent literature optical and near-infrared determinations within the uncertainties. We argue that 2MASS is biased against low surface brightness galaxies, and use SDSS plus our knowledge of stellar populations to estimate that the true K-band luminosity function has a steeper faint end slope than the direct estimate. Assuming a universally-applicable stellar initial mass function (IMF), we derive the stellar mass function of galaxies. The faint end slope slope for the stellar mass function is steeper than -1.1, reflecting the low stellar M/Ls characteristic of low-mass galaxies. We estimate an upper limit to the stellar mass density in the local Universe Omega* h = 0.0020+/-0.0006 by assuming an IMF as rich in low-mass stars as allowed by observations of galaxy dynamics. Finally, we find that the characteristic luminosity or mass of early-type galaxies is larger than for later types, and the faint end slope is steeper for later types than for earlier types. Accounting for typing uncertainties, we estimate that at least half, and perhaps as much as 3/4, of the stellar mass in the Universe is in early-type galaxies. We present also SDSS/2MASS color-M/L correlations, an updated discussion of near-infrared stellar M/L estimates, and the volume-corrected distribution of g and K-band stellar M/Ls as a function of stellar mass. [Abridged]

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arXiv2003

The Clustering Dipole of the Local Universe from the Two Micron All Sky Survey

The unprecedented sky coverage and photometric uniformity of the Two Micron All Sky Survey (2MASS) provides a rich resource for investigating the galaxies populating the local Universe. A full characterization of the large-scale clustering distribution is important for theoretical studies of structure formation. 2MASS offers an all-sky view of the local galaxy population at 2.15 micron, unbiased by young stellar light and minimally affected by dust. We use 2MASS to map the local distribution of galaxies, identifying the largest structures in the nearby universe. The inhomogeneity of these structures causes an acceleration on the Local Group of galaxies, which can be seen in the dipole of the Cosmic Microwave Background (CMB). We find that the direction of the 2MASS clustering dipole is 11 degrees from the CMB dipole, confirming that the local galaxy distribution accelerates the Local Group. From the magnitude of the dipole we find a value of the linear bias parameter b=1.37 +/- 0.3 in the K_s-band. The 2MASS clustering dipole is 19 degrees from the latest measurement of the dipole using galaxies detected by the Infrared Astronomical Satellite (IRAS) suggesting that bias may be non-linear in some wavebands.

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