Helene Courtois | University of Lyon (original) (raw)
Papers by Helene Courtois
The work presented in this paper aims at restricting the input parameter values of the semi-analy... more The work presented in this paper aims at restricting the input parameter values of the semi-analytical model used in Galics and MoMaF, so as to derive which parameters influence the most the results, e.g., star formation, feedback and halo recycling eciencies, etc. Our approach is to proceed empirically: we run lots of simulations and derive the correct ranges of values.
The neutral hydrogen properties of 1,822 galaxies are being studied with the Green Bank 100m and ... more The neutral hydrogen properties of 1,822 galaxies are being studied with the Green Bank 100m and the Parkes 64m telescopes as part of the 'Cosmic Flows' program. Observed parameters include systemic velocities, profile line widths, and fluxes. The line width information can be combined with optical and infrared photometry to obtain distances. The 1,822 HI observations complement an inventory of
The peculiar velocities of galaxies are responding to the distribution of matter over a wide rang... more The peculiar velocities of galaxies are responding to the distribution of matter over a wide range of scales. A proper understanding of the forces at play requires the measurement of distances with the highest possible sampling density. A preliminary analysis [14] with 1,252 accurate distances demonstrates dramatically that a significant component of our motion reflected in the Cosmic Microwave Background
This paper presents MoLUSC, a new method for generating mock galaxy catalogs from a large scale (... more This paper presents MoLUSC, a new method for generating mock galaxy catalogs from a large scale ($\approx 1000^3$ Mpc$^3$) dark matter simulation, that requires only modest CPU time and memory allocation. The method uses a small-scale ($\approx 256^3$ Mpc$^3$) dark matter simulation on which the \galics semi-analytic code has been run in order to define the transformation from dark matter
The length of the three-dimensional filaments observed in the fourth public data-release of the S... more The length of the three-dimensional filaments observed in the fourth public data-release of the SDSS is measured using the {\em local skeleton} method. It consists in defining the set of points where the gradient of the smoothed density field is extremal along its isocontours, with some additional constraints on local curvature to probe actual ridges in the galaxy distribution. A
The Astrophysical Journal Supplement Series, 2015
The Spitzer Survey of Stellar Structure in Galaxies (S 4 G) is the largest available database of ... more The Spitzer Survey of Stellar Structure in Galaxies (S 4 G) is the largest available database of deep, homogeneous middle-infrared (mid-IR) images of galaxies of all types. The survey, which includes 2352 nearby galaxies, reveals galaxy morphology only minimally affected by interstellar extinction. This paper presents an atlas and classifications of S 4 G galaxies in the Comprehensive de Vaucouleurs revised Hubble-Sandage (CVRHS) system. The CVRHS system follows the precepts of classical de Vaucouleurs (1959) morphology, modified to include recognition of other features such as inner, outer, and nuclear lenses, nuclear rings, bars, and disks, spheroidal galaxies, X patterns and box/peanut structures, OLR subclass outer rings and pseudorings, bar ansae and barlenses, parallel sequence late-types, thick disks, and embedded disks in 3D early-type systems. We show that our CVRHS classifications are internally consistent, and that nearly half of the S 4 G sample consists of extreme late-type systems (mostly bulgeless, pure disk galaxies) in the range Scd-Im. The most common family classification for mid-IR types S0/a to Sc is SA while that for types Scd to Sm is SB. The bars in these two type domains are very different in mid-IR structure and morphology. This paper examines the bar, ring, and type classification fractions in the sample, and also includes several montages of images highlighting the various kinds of "stellar structures" seen in mid-IR galaxy morphology.
Nature, 2014
Galaxies congregate in clusters and along filaments, and are missing from large regions referred ... more Galaxies congregate in clusters and along filaments, and are missing from large regions referred to as voids. These structures are seen in maps derived from spectroscopic surveys 1,2 that reveal networks of structure that are interconnected with no clear boundaries. Extended regions with a high concentration of galaxies are called 'superclusters', although this term is not precise. There is, however, another way to analyse the structure. If the distance to each galaxy from Earth is directly measured, then the peculiar velocity can be derived from the subtraction of the mean cosmic expansion, the product of distance times the Hubble constant, from observed velocity. The peculiar velocity is the line-of-sight departure from the cosmic expansion and arises from gravitational perturbations; a map of peculiar velocities can be translated into a map of the distribution of matter 3 . Here we report a map of structure made using a catalogue of peculiar velocities. We find locations where peculiar velocity flows diverge, as water does at watershed divides, and we trace the surface of divergent points that surrounds us. Within the volume enclosed by this surface, the motions of galaxies are inward after removal of the mean cosmic expansion and long range flows. We define a supercluster to be the volume within such a surface, and so we are defining the extent of our home supercluster, which we call Laniakea.
A database can be accessed on the web at http://edd.ifa.hawaii.edu that was developed to promote ... more A database can be accessed on the web at http://edd.ifa.hawaii.edu that was developed to promote access to information related to galaxy distances. The database has three functional components. First, tables from many literature sources have been gathered and enhanced with links through a distinct galaxy naming convention. Second, comparisons of results both at the levels of parameters and of techniques
2007 IEEE International Parallel and Distributed Processing Symposium, 2007
Les problèmes à large échelle issus de la simulation numérique peuvent désormais être résolus sur... more Les problèmes à large échelle issus de la simulation numérique peuvent désormais être résolus sur des serveurs distants en utilisant des intergiciels de grille. Ce rapport décrit les différentes étapes nécessaires pour "gridifier" une application en utilisant l'intergiciel DIET. Les détails de la mise en oeuvre sont décrits au travers de l'application de cosmologie appelée RAMSES. Enfin, nous montrerons expérimentalement les avantages de cette approche, parmi lesquels une utilisation transparente des ressources pour un faible coût.
The Astrophysical Journal, 2011
We notice that nearby galaxies having high negative peculiar velocities are distributed over the ... more We notice that nearby galaxies having high negative peculiar velocities are distributed over the sky very inhomogeneously. A part of this anisotropy is caused by the "Local Velocity Anomaly", i.e. by the bulk motion of nearby galaxies away from the Local Void. But a half of the fast-flying objects reside within a small region [RA = 11.5 h − 13.0 h , Dec. = +20 • − +40 • ], known as the Coma I cloud. According to , this complex contains 8 groups, 5 triplets, 10 pairs and 83 single galaxies with the total mass of 4.7 · 10 13 M ⊙ .
![Research paper thumbnail of Erratum: “Our Peculiar Motion Away from the Local Void” (ApJ, 676, 184 [2008])](https://attachments.academia-assets.com/44112977/thumbnails/1.jpg)
](The Astrophysical Journal, 2008
The Astrophysical Journal, 2012
This paper presents an analysis of the local peculiar velocity field based on the Wiener Filter (... more This paper presents an analysis of the local peculiar velocity field based on the Wiener Filter (WF) reconstruction method. We used our currently available catalog of distance measurements containing 1797 galaxies within 3000 km s −1 : Cosmicflows-1. The WF method is used to recover the full three-dimensional peculiar velocity field from the observed map of radial velocities and to recover the underlying linear density field. The velocity field within a data zone of 3000 km s −1 is decomposed into a local component that is generated within the data zone and a tidal one that is generated by the mass distribution outside that zone. The tidal component is characterized by a coherent flow toward the Norma-Hydra-Centaurus (Great Attractor) region, while the local component is dominated by a flow toward the Virgo Cluster and away from the Local Void. A detailed analysis shows that the local flow is predominantly governed by the Local Void and the Virgo Cluster plays a lesser role. The analysis procedure was tested against a mock catalog. It is demonstrated that the WF accurately recovers the input velocity field of the mock catalog on the scale of the extraction of distances and reasonably recovers the velocity field on significantly larger scales. The Bayesian WF reconstruction is carried out within the ΛCDM WMAP5 framework. The WF reconstruction draws particular attention to the importance of voids in proximity to our neighborhood. The prominent structure of the Local Supercluster is wrapped in a horseshoe collar of under density with the Local Void as a major component.
The Astrophysical Journal, 2008
The peculiar velocity of the Local Group of galaxies manifested in the Cosmic Microwave Backgroun... more The peculiar velocity of the Local Group of galaxies manifested in the Cosmic Microwave Background dipole is found to decompose into three dominant components. The three components are clearly separated because they arise on distinct spatial scales and are fortuitously almost orthogonal in their influences. The nearest, which is distinguished by a velocity discontinuity at ∼ 7 Mpc, arises from the evacuation of the Local Void. We lie in the Local Sheet that bounds the void. Random motions within the Local Sheet are small and we advocate a reference frame with respect to the Local Sheet in preference to the Local Group. Our Galaxy participates in the bulk motion of the Local Sheet away from the Local Void. The component of our motion on an intermediate scale is attributed to the Virgo Cluster and its surroundings, 17 Mpc away. The third and largest component is an attraction on scales larger than 3000 km s −1 and centered near the direction of the Centaurus Cluster. The amplitudes of the three components are 259, 185, and 455 km s −1 , respectively, adding collectively to 631 km s −1 in the reference frame of the Local Sheet. Taking the nearby influences into account, particularly that of the Local Void, causes the residual attributed to large scales to align with observed concentrations of distant galaxies and reduces somewhat the amplitude of motion attributed to their pull. Turning to small scales, in addition to the motion of our Local Sheet away from the Local Void, the nearest adjacent filament, the Leo Spur, is seen to be moving in a direction that will lead to convergence with our filament. Finally, a good distance to an isolated galaxy within the Local Void reveals that this dwarf system has a substantial motion of at least 230 km s −1 away from the void center. Given the velocities expected from gravitational instability theory in the standard cosmological paradigm, the distance to the center of the Local Void must be at least 23 Mpc from our position, implying the Local Void is extremely large.
The Astronomical Journal, 2014
We combine data from the Spitzer Survey for Stellar Structure in Galaxies (S 4 G), a recently cal... more We combine data from the Spitzer Survey for Stellar Structure in Galaxies (S 4 G), a recently calibrated empirical stellar mass estimator from Eskew et al., and an extensive database of HI spectral line profiles to examine the baryonic Tully-Fisher (BTF) relation. We find 1) that the BTF has lower scatter than the classic Tully-Fisher (TF) relation and is better described as a linear relationship, confirming similar previous results, 2) that the inclusion of a radial scale in the BTF decreases the scatter but only modestly, as seen previously for the TF relation, and 3) that the slope of the BTF, which we find to be 3.5 ± 0.2 (∆ log M baryon /∆ log v c ), implies that on average a nearly constant fraction (∼ 0.4) of all baryons expected to be in a halo are "condensed" onto the central region of rotationally supported galaxies. The condensed baryon fraction, M baryon /M total , is, to our measurement precision, nearly independent of galaxy circular velocity (our sample spans circular velocities, v c , between 60 and 250 km s −1 , but is extended to v c ∼ 10 km s −1 using data from the literature). The observed galaxy-to-galaxy scatter in this fraction is generally ≤ a factor of 2 despite fairly liberal selection criteria. These results imply that cooling and heating processes, such as cold vs. hot accretion, mass loss due to stellar winds, and AGN driven feedback, to the degree that they affect the global galactic properties involved in the BTF, are independent of halo mass for galaxies with 10 < v c < 250 km s −1 and typically introduce no more than a factor of two range in the resulting M baryon /M total . Recent simulations by Aumer et al. of a small sample of disk galaxies are in excellent agreement with our data, suggesting that current simulations are capable of reproducing the global properties of individual disk galaxies. More detailed comparison to models using the BTF holds great promise, but awaits improved determinations of the stellar masses.
The Astronomical Journal, 2009
A database can be accessed on the web at http://edd.ifa.hawaii.edu that was developed to promote ... more A database can be accessed on the web at http://edd.ifa.hawaii.edu that was developed to promote access to information related to galaxy distances. The database has three functional components. First, tables from many literature sources have been gathered and enhanced with links through a distinct galaxy naming convention. Second, comparisons of results both at the levels of parameters and of techniques have begun and are continuing, leading to increasing homogeneity and consistency of distance measurements. Third, new material are presented arising from ongoing observational programs at the University of Hawaii 2.2m telescope, radio telescopes at Green Bank, Arecibo, and Parkes and with Hubble Space Telescope. This new observational material is made available in tandem with related material drawn from archives and passed through common analysis pipelines.
It is astonishing that only 30% of the motion of our Galaxy is understood, a fact that highlights... more It is astonishing that only 30% of the motion of our Galaxy is understood, a fact that highlights a fundamental deficiency in our understanding of the composition of the Universe. Spitzer Cosmic Flows is the photometric component of a program to map the peculiar motions and large-scale flows of galaxies out to 200 Mpc in order to constrain the distribution of mass. This task requires measuring the peculiar velocity of galaxies, a response to the distribution of both baryonic and dark matter, densely sampled over the full sky. With an independent distance measurement, an observed galaxy redshift can be separated into cosmic expansion and peculiar velocity components. Spitzer Cosmic Flows will use IRAC 3.6 micron imaging to obtain independent distances using the correlation between galaxy luminosity and rotation rate (the mid-IR Tully-Fisher relation). The rotational velocity data is being acquired through the Cosmic Flows Large Program on the NRAO Green Bank Telescope and a complemen...
Monthly Notices of the Royal Astronomical Society: Letters, 2005
We present predictions for the abundance of Ly-α emitters in hierarchical structure formation mod... more We present predictions for the abundance of Ly-α emitters in hierarchical structure formation models. We use the GALFORM semi-analytical model of galaxy formation to explore the impact on the predicted counts of varying assumptions about the escape fraction of Ly-α photons, the redshift at which the universe reionized and the cosmological density parameter. A model with a fixed escape fraction gives a remarkably good match to the observed counts over a wide redshift interval. The counts at bright fluxes are dominated by ongoing starbursts. We present predictions for the expected counts in a typical observation with the Multi-Unit Spectroscopic Explorer (MUSE) instrument proposed for the Very Large Telescope.
Monthly Notices of the Royal Astronomical Society, 2011
The neutral hydrogen properties of 1,822 galaxies are being studied with the Green Bank 100m and ... more The neutral hydrogen properties of 1,822 galaxies are being studied with the Green Bank 100m and the Parkes 64m telescopes as part of the 'Cosmic Flows' program. Observed parameters include systemic velocities, profile line widths, and integrated fluxes. The line width information can be combined with optical and infrared photometry to obtain distances. The 1,822 HI observations complement an inventory of archives. All told, HI line width information is available for almost all of five samples: (i) luminosity-line width correlation calibrators, (ii) zero-point calibrators for the supernova Ia scale, (iii) a dense local sample of spiral galaxies with M Ks < −21 within 3,000 km s −1 , (iv) a sparser sample of 60 µm selected galaxies within 6,000 km s −1 that provides all-sky coverage of our extended supercluster complex, and (v) an even sparser sample of flat galaxies, extreme edge-on spirals, extending in a volume out to 12,000 km s −1 . The HI information for 13,941 galaxies, whether from the archives or acquired as part of the Cosmic Flows observational program, is uniformly re-measured and made available through the Extragalactic Distance Database web site.
Astronomy and astrophysics: A European journal, 2004
Información del artículo The LEDA galaxy distribution. I. Maps of the local universe.
Publications of the Astronomical Society of the Pacific, 2010
The mid-infrared is an optimal window to trace stellar mass in nearby galaxies and the 3.6µm IRAC... more The mid-infrared is an optimal window to trace stellar mass in nearby galaxies and the 3.6µm IRAC band has been exploited to this effect, but such mass estimates can be biased by dust emission. We present our pipeline to reveal the old stellar flux at 3.6µm and obtain stellar mass maps for more than 1600 galaxies available from the Spitzer Survey of Stellar Structure in Galaxies (S 4 G). This survey consists of images in two infrared bands (3.6 and 4.5µm), and we use the Independent Component Analysis (ICA) method presented in to separate the dominant light from old stars and the dust emission that can significantly contribute to the observed 3.6µm flux. We exclude from our ICA analysis galaxies with low signal-to-noise (S/N < 10) and those with original [3.6]-[4.5] colors compatible with an old stellar population, indicative of little dust emission (mostly early Hubble types, which can directly provide good mass maps). For the remaining 1251 galaxies to which ICA was successfully applied, we find that as much as 10-30% of the total light at 3.6µm typically originates from dust, and locally it can reach even higher values. This contamination fraction shows a correlation with specific star formation rates, confirming that the dust emission that we detect is related to star formation. Additionally, we have used our large sample of mass estimates to calibrate a relationship of effective M/L as a function of observed [3.6]-[4.5] color: log(M/L) = −0.339(±0.057) × ([3.6] − [4.5]) − 0.336(±0.002). Our final pipeline products will be made public through IRSA, providing the astronomical community with an unprecedentedly large set of stellar mass maps ready to use for scientific applications.
The work presented in this paper aims at restricting the input parameter values of the semi-analy... more The work presented in this paper aims at restricting the input parameter values of the semi-analytical model used in Galics and MoMaF, so as to derive which parameters influence the most the results, e.g., star formation, feedback and halo recycling eciencies, etc. Our approach is to proceed empirically: we run lots of simulations and derive the correct ranges of values.
The neutral hydrogen properties of 1,822 galaxies are being studied with the Green Bank 100m and ... more The neutral hydrogen properties of 1,822 galaxies are being studied with the Green Bank 100m and the Parkes 64m telescopes as part of the 'Cosmic Flows' program. Observed parameters include systemic velocities, profile line widths, and fluxes. The line width information can be combined with optical and infrared photometry to obtain distances. The 1,822 HI observations complement an inventory of
The peculiar velocities of galaxies are responding to the distribution of matter over a wide rang... more The peculiar velocities of galaxies are responding to the distribution of matter over a wide range of scales. A proper understanding of the forces at play requires the measurement of distances with the highest possible sampling density. A preliminary analysis [14] with 1,252 accurate distances demonstrates dramatically that a significant component of our motion reflected in the Cosmic Microwave Background
This paper presents MoLUSC, a new method for generating mock galaxy catalogs from a large scale (... more This paper presents MoLUSC, a new method for generating mock galaxy catalogs from a large scale ($\approx 1000^3$ Mpc$^3$) dark matter simulation, that requires only modest CPU time and memory allocation. The method uses a small-scale ($\approx 256^3$ Mpc$^3$) dark matter simulation on which the \galics semi-analytic code has been run in order to define the transformation from dark matter
The length of the three-dimensional filaments observed in the fourth public data-release of the S... more The length of the three-dimensional filaments observed in the fourth public data-release of the SDSS is measured using the {\em local skeleton} method. It consists in defining the set of points where the gradient of the smoothed density field is extremal along its isocontours, with some additional constraints on local curvature to probe actual ridges in the galaxy distribution. A
The Astrophysical Journal Supplement Series, 2015
The Spitzer Survey of Stellar Structure in Galaxies (S 4 G) is the largest available database of ... more The Spitzer Survey of Stellar Structure in Galaxies (S 4 G) is the largest available database of deep, homogeneous middle-infrared (mid-IR) images of galaxies of all types. The survey, which includes 2352 nearby galaxies, reveals galaxy morphology only minimally affected by interstellar extinction. This paper presents an atlas and classifications of S 4 G galaxies in the Comprehensive de Vaucouleurs revised Hubble-Sandage (CVRHS) system. The CVRHS system follows the precepts of classical de Vaucouleurs (1959) morphology, modified to include recognition of other features such as inner, outer, and nuclear lenses, nuclear rings, bars, and disks, spheroidal galaxies, X patterns and box/peanut structures, OLR subclass outer rings and pseudorings, bar ansae and barlenses, parallel sequence late-types, thick disks, and embedded disks in 3D early-type systems. We show that our CVRHS classifications are internally consistent, and that nearly half of the S 4 G sample consists of extreme late-type systems (mostly bulgeless, pure disk galaxies) in the range Scd-Im. The most common family classification for mid-IR types S0/a to Sc is SA while that for types Scd to Sm is SB. The bars in these two type domains are very different in mid-IR structure and morphology. This paper examines the bar, ring, and type classification fractions in the sample, and also includes several montages of images highlighting the various kinds of "stellar structures" seen in mid-IR galaxy morphology.
Nature, 2014
Galaxies congregate in clusters and along filaments, and are missing from large regions referred ... more Galaxies congregate in clusters and along filaments, and are missing from large regions referred to as voids. These structures are seen in maps derived from spectroscopic surveys 1,2 that reveal networks of structure that are interconnected with no clear boundaries. Extended regions with a high concentration of galaxies are called 'superclusters', although this term is not precise. There is, however, another way to analyse the structure. If the distance to each galaxy from Earth is directly measured, then the peculiar velocity can be derived from the subtraction of the mean cosmic expansion, the product of distance times the Hubble constant, from observed velocity. The peculiar velocity is the line-of-sight departure from the cosmic expansion and arises from gravitational perturbations; a map of peculiar velocities can be translated into a map of the distribution of matter 3 . Here we report a map of structure made using a catalogue of peculiar velocities. We find locations where peculiar velocity flows diverge, as water does at watershed divides, and we trace the surface of divergent points that surrounds us. Within the volume enclosed by this surface, the motions of galaxies are inward after removal of the mean cosmic expansion and long range flows. We define a supercluster to be the volume within such a surface, and so we are defining the extent of our home supercluster, which we call Laniakea.
A database can be accessed on the web at http://edd.ifa.hawaii.edu that was developed to promote ... more A database can be accessed on the web at http://edd.ifa.hawaii.edu that was developed to promote access to information related to galaxy distances. The database has three functional components. First, tables from many literature sources have been gathered and enhanced with links through a distinct galaxy naming convention. Second, comparisons of results both at the levels of parameters and of techniques
2007 IEEE International Parallel and Distributed Processing Symposium, 2007
Les problèmes à large échelle issus de la simulation numérique peuvent désormais être résolus sur... more Les problèmes à large échelle issus de la simulation numérique peuvent désormais être résolus sur des serveurs distants en utilisant des intergiciels de grille. Ce rapport décrit les différentes étapes nécessaires pour "gridifier" une application en utilisant l'intergiciel DIET. Les détails de la mise en oeuvre sont décrits au travers de l'application de cosmologie appelée RAMSES. Enfin, nous montrerons expérimentalement les avantages de cette approche, parmi lesquels une utilisation transparente des ressources pour un faible coût.
The Astrophysical Journal, 2011
We notice that nearby galaxies having high negative peculiar velocities are distributed over the ... more We notice that nearby galaxies having high negative peculiar velocities are distributed over the sky very inhomogeneously. A part of this anisotropy is caused by the "Local Velocity Anomaly", i.e. by the bulk motion of nearby galaxies away from the Local Void. But a half of the fast-flying objects reside within a small region [RA = 11.5 h − 13.0 h , Dec. = +20 • − +40 • ], known as the Coma I cloud. According to , this complex contains 8 groups, 5 triplets, 10 pairs and 83 single galaxies with the total mass of 4.7 · 10 13 M ⊙ .
The Astrophysical Journal, 2008
The Astrophysical Journal, 2012
This paper presents an analysis of the local peculiar velocity field based on the Wiener Filter (... more This paper presents an analysis of the local peculiar velocity field based on the Wiener Filter (WF) reconstruction method. We used our currently available catalog of distance measurements containing 1797 galaxies within 3000 km s −1 : Cosmicflows-1. The WF method is used to recover the full three-dimensional peculiar velocity field from the observed map of radial velocities and to recover the underlying linear density field. The velocity field within a data zone of 3000 km s −1 is decomposed into a local component that is generated within the data zone and a tidal one that is generated by the mass distribution outside that zone. The tidal component is characterized by a coherent flow toward the Norma-Hydra-Centaurus (Great Attractor) region, while the local component is dominated by a flow toward the Virgo Cluster and away from the Local Void. A detailed analysis shows that the local flow is predominantly governed by the Local Void and the Virgo Cluster plays a lesser role. The analysis procedure was tested against a mock catalog. It is demonstrated that the WF accurately recovers the input velocity field of the mock catalog on the scale of the extraction of distances and reasonably recovers the velocity field on significantly larger scales. The Bayesian WF reconstruction is carried out within the ΛCDM WMAP5 framework. The WF reconstruction draws particular attention to the importance of voids in proximity to our neighborhood. The prominent structure of the Local Supercluster is wrapped in a horseshoe collar of under density with the Local Void as a major component.
The Astrophysical Journal, 2008
The peculiar velocity of the Local Group of galaxies manifested in the Cosmic Microwave Backgroun... more The peculiar velocity of the Local Group of galaxies manifested in the Cosmic Microwave Background dipole is found to decompose into three dominant components. The three components are clearly separated because they arise on distinct spatial scales and are fortuitously almost orthogonal in their influences. The nearest, which is distinguished by a velocity discontinuity at ∼ 7 Mpc, arises from the evacuation of the Local Void. We lie in the Local Sheet that bounds the void. Random motions within the Local Sheet are small and we advocate a reference frame with respect to the Local Sheet in preference to the Local Group. Our Galaxy participates in the bulk motion of the Local Sheet away from the Local Void. The component of our motion on an intermediate scale is attributed to the Virgo Cluster and its surroundings, 17 Mpc away. The third and largest component is an attraction on scales larger than 3000 km s −1 and centered near the direction of the Centaurus Cluster. The amplitudes of the three components are 259, 185, and 455 km s −1 , respectively, adding collectively to 631 km s −1 in the reference frame of the Local Sheet. Taking the nearby influences into account, particularly that of the Local Void, causes the residual attributed to large scales to align with observed concentrations of distant galaxies and reduces somewhat the amplitude of motion attributed to their pull. Turning to small scales, in addition to the motion of our Local Sheet away from the Local Void, the nearest adjacent filament, the Leo Spur, is seen to be moving in a direction that will lead to convergence with our filament. Finally, a good distance to an isolated galaxy within the Local Void reveals that this dwarf system has a substantial motion of at least 230 km s −1 away from the void center. Given the velocities expected from gravitational instability theory in the standard cosmological paradigm, the distance to the center of the Local Void must be at least 23 Mpc from our position, implying the Local Void is extremely large.
The Astronomical Journal, 2014
We combine data from the Spitzer Survey for Stellar Structure in Galaxies (S 4 G), a recently cal... more We combine data from the Spitzer Survey for Stellar Structure in Galaxies (S 4 G), a recently calibrated empirical stellar mass estimator from Eskew et al., and an extensive database of HI spectral line profiles to examine the baryonic Tully-Fisher (BTF) relation. We find 1) that the BTF has lower scatter than the classic Tully-Fisher (TF) relation and is better described as a linear relationship, confirming similar previous results, 2) that the inclusion of a radial scale in the BTF decreases the scatter but only modestly, as seen previously for the TF relation, and 3) that the slope of the BTF, which we find to be 3.5 ± 0.2 (∆ log M baryon /∆ log v c ), implies that on average a nearly constant fraction (∼ 0.4) of all baryons expected to be in a halo are "condensed" onto the central region of rotationally supported galaxies. The condensed baryon fraction, M baryon /M total , is, to our measurement precision, nearly independent of galaxy circular velocity (our sample spans circular velocities, v c , between 60 and 250 km s −1 , but is extended to v c ∼ 10 km s −1 using data from the literature). The observed galaxy-to-galaxy scatter in this fraction is generally ≤ a factor of 2 despite fairly liberal selection criteria. These results imply that cooling and heating processes, such as cold vs. hot accretion, mass loss due to stellar winds, and AGN driven feedback, to the degree that they affect the global galactic properties involved in the BTF, are independent of halo mass for galaxies with 10 < v c < 250 km s −1 and typically introduce no more than a factor of two range in the resulting M baryon /M total . Recent simulations by Aumer et al. of a small sample of disk galaxies are in excellent agreement with our data, suggesting that current simulations are capable of reproducing the global properties of individual disk galaxies. More detailed comparison to models using the BTF holds great promise, but awaits improved determinations of the stellar masses.
The Astronomical Journal, 2009
A database can be accessed on the web at http://edd.ifa.hawaii.edu that was developed to promote ... more A database can be accessed on the web at http://edd.ifa.hawaii.edu that was developed to promote access to information related to galaxy distances. The database has three functional components. First, tables from many literature sources have been gathered and enhanced with links through a distinct galaxy naming convention. Second, comparisons of results both at the levels of parameters and of techniques have begun and are continuing, leading to increasing homogeneity and consistency of distance measurements. Third, new material are presented arising from ongoing observational programs at the University of Hawaii 2.2m telescope, radio telescopes at Green Bank, Arecibo, and Parkes and with Hubble Space Telescope. This new observational material is made available in tandem with related material drawn from archives and passed through common analysis pipelines.
It is astonishing that only 30% of the motion of our Galaxy is understood, a fact that highlights... more It is astonishing that only 30% of the motion of our Galaxy is understood, a fact that highlights a fundamental deficiency in our understanding of the composition of the Universe. Spitzer Cosmic Flows is the photometric component of a program to map the peculiar motions and large-scale flows of galaxies out to 200 Mpc in order to constrain the distribution of mass. This task requires measuring the peculiar velocity of galaxies, a response to the distribution of both baryonic and dark matter, densely sampled over the full sky. With an independent distance measurement, an observed galaxy redshift can be separated into cosmic expansion and peculiar velocity components. Spitzer Cosmic Flows will use IRAC 3.6 micron imaging to obtain independent distances using the correlation between galaxy luminosity and rotation rate (the mid-IR Tully-Fisher relation). The rotational velocity data is being acquired through the Cosmic Flows Large Program on the NRAO Green Bank Telescope and a complemen...
Monthly Notices of the Royal Astronomical Society: Letters, 2005
We present predictions for the abundance of Ly-α emitters in hierarchical structure formation mod... more We present predictions for the abundance of Ly-α emitters in hierarchical structure formation models. We use the GALFORM semi-analytical model of galaxy formation to explore the impact on the predicted counts of varying assumptions about the escape fraction of Ly-α photons, the redshift at which the universe reionized and the cosmological density parameter. A model with a fixed escape fraction gives a remarkably good match to the observed counts over a wide redshift interval. The counts at bright fluxes are dominated by ongoing starbursts. We present predictions for the expected counts in a typical observation with the Multi-Unit Spectroscopic Explorer (MUSE) instrument proposed for the Very Large Telescope.
Monthly Notices of the Royal Astronomical Society, 2011
The neutral hydrogen properties of 1,822 galaxies are being studied with the Green Bank 100m and ... more The neutral hydrogen properties of 1,822 galaxies are being studied with the Green Bank 100m and the Parkes 64m telescopes as part of the 'Cosmic Flows' program. Observed parameters include systemic velocities, profile line widths, and integrated fluxes. The line width information can be combined with optical and infrared photometry to obtain distances. The 1,822 HI observations complement an inventory of archives. All told, HI line width information is available for almost all of five samples: (i) luminosity-line width correlation calibrators, (ii) zero-point calibrators for the supernova Ia scale, (iii) a dense local sample of spiral galaxies with M Ks < −21 within 3,000 km s −1 , (iv) a sparser sample of 60 µm selected galaxies within 6,000 km s −1 that provides all-sky coverage of our extended supercluster complex, and (v) an even sparser sample of flat galaxies, extreme edge-on spirals, extending in a volume out to 12,000 km s −1 . The HI information for 13,941 galaxies, whether from the archives or acquired as part of the Cosmic Flows observational program, is uniformly re-measured and made available through the Extragalactic Distance Database web site.
Astronomy and astrophysics: A European journal, 2004
Información del artículo The LEDA galaxy distribution. I. Maps of the local universe.
Publications of the Astronomical Society of the Pacific, 2010
The mid-infrared is an optimal window to trace stellar mass in nearby galaxies and the 3.6µm IRAC... more The mid-infrared is an optimal window to trace stellar mass in nearby galaxies and the 3.6µm IRAC band has been exploited to this effect, but such mass estimates can be biased by dust emission. We present our pipeline to reveal the old stellar flux at 3.6µm and obtain stellar mass maps for more than 1600 galaxies available from the Spitzer Survey of Stellar Structure in Galaxies (S 4 G). This survey consists of images in two infrared bands (3.6 and 4.5µm), and we use the Independent Component Analysis (ICA) method presented in to separate the dominant light from old stars and the dust emission that can significantly contribute to the observed 3.6µm flux. We exclude from our ICA analysis galaxies with low signal-to-noise (S/N < 10) and those with original [3.6]-[4.5] colors compatible with an old stellar population, indicative of little dust emission (mostly early Hubble types, which can directly provide good mass maps). For the remaining 1251 galaxies to which ICA was successfully applied, we find that as much as 10-30% of the total light at 3.6µm typically originates from dust, and locally it can reach even higher values. This contamination fraction shows a correlation with specific star formation rates, confirming that the dust emission that we detect is related to star formation. Additionally, we have used our large sample of mass estimates to calibrate a relationship of effective M/L as a function of observed [3.6]-[4.5] color: log(M/L) = −0.339(±0.057) × ([3.6] − [4.5]) − 0.336(±0.002). Our final pipeline products will be made public through IRSA, providing the astronomical community with an unprecedentedly large set of stellar mass maps ready to use for scientific applications.