Amanda Bauer - Academia.edu (original) (raw)

Papers by Amanda Bauer

The GOODS NICMOS Survey is a large Hubble Space Telescope programme to obtain deep H-band and J-b... more The GOODS NICMOS Survey is a large Hubble Space Telescope programme to obtain deep H-band and J-band imaging over the GOODS-North and South fields. The total exposure time is 180 orbits within the F160W filter (H-band) in fields surrounding massive galaxies with log M>11 at 2>z<3. This survey covers 1/3 of a GOODS field, and reaches a depth of H

We present a study of the relationship between galaxy colour, stellar mass, and local galaxy dens... more We present a study of the relationship between galaxy colour, stellar mass, and local galaxy density in a deep near-infrared imaging survey up to a redshift of z~3 using the GOODS NICMOS Survey (GNS). The GNS is a very deep, near-infrared Hubble Space Telescope survey imaging a total of 45 arcmin^2 in the GOODS fields, reaching a stellar mass completeness

Monthly Notices of the Royal Astronomical Society, 2015

We present the GAMA Panchromatic Data Release (PDR) constituting over 230deg 2 of imaging with ph... more We present the GAMA Panchromatic Data Release (PDR) constituting over 230deg 2 of imaging with photometry in 21 bands extending from the far-UV to the far-IR. These data complement our spectroscopic campaign of over 300k galaxies, and are compiled from observations with a variety of facilities including: GALEX, SDSS, VISTA, WISE, and Herschel, with the GAMA regions currently being surveyed by VST and scheduled for observations by ASKAP. These data are processed to a common astrometric solution, from which photometry is derived for ∼ 221, 373 galaxies with r < 19.8 mag. Online tools are provided to access and download data cutouts, or the full mosaics of the GAMA regions in each band.

Multiwavelength AGN Surveys - Proceedings of the Guillermo Haro Conference 2003, 2004

The Universe became fully reionized, and observable optically, at a time corresponding to redshif... more The Universe became fully reionized, and observable optically, at a time corresponding to redshift z ∼ 6.5, so it is only by studying the HI and molecular absorption lines against higher-redshift, radio-loud sources that one can hope to make detailed studies of the earliest stages of galaxy formation. At present no targets for such studies are known. In these proceedings we describe a survey which is underway to find radio-loud quasars at z > 6.5, and present broad-band SEDs of our most promising candidates.

Ground-based and Airborne Instrumentation for Astronomy IV, 2012

SAMI (Sydney-AAO Multi-object Integral field spectrograph) has the potential to revolutionise our... more SAMI (Sydney-AAO Multi-object Integral field spectrograph) has the potential to revolutionise our understanding of galaxies, with spatially-resolved spectroscopy of large numbers of targets. It is the first on-sky application of innovative photonic imaging bundles called hexabundles, which will remove the aperture effects that have biased previous single-fibre multi-object astronomical surveys. The hexabundles have lightly-fused circular multi-mode cores with a covering fraction of ∼ 73%. The thirteen hexabundles in SAMI, each have 61 fibre cores, and feed into the AAOmega spectrograph at the Anglo-Australian Telescope (AAT). SAMI was installed at the AAT in July 2011 and the first commissioning results prove the effectiveness of hexabundles on sky. A galaxy survey of several thousand galaxies to z ∼ 0.1 will begin with SAMI in mid-2012.

The Astrophysical Journal, 2012

We present the first scientific results from the Sydney-AAO Multi-Object IFS (SAMI) at the Anglo-... more We present the first scientific results from the Sydney-AAO Multi-Object IFS (SAMI) at the Anglo-Australian Telescope. This unique instrument deploys 13 fused fibre bundles (hexabundles) across a one-degree field of view allowing simultaneous spatially-resolved spectroscopy of 13 galaxies. During the first SAMI commissioning run, targeting a single galaxy field, one object (ESO 185-G031) was found to have extended minor axis emission with ionisation and kinematic properties consistent with a large-scale galactic wind. The importance of this result is two-fold: (i) fibre bundle spectrographs are able to identify low-surface brightness emission arising from extranuclear activity; (ii) such activity may be more common than presently assumed because conventional multi-object spectrographs use single-aperture fibres and spectra from these are nearly always dominated by nuclear emission. These early results demonstrate the extraordinary potential of multi-object hexabundle spectroscopy in future galaxy surveys.

The Astrophysical Journal, 2012

... up stellar matter in their outer regions (see, eg, Trujillo et al. 2007; Buitrago et al. 2008... more ... up stellar matter in their outer regions (see, eg, Trujillo et al. 2007; Buitrago et al. 2008; Cimatti et al. 2008; van Dokkum et al. 2009; Carrasco et al. 2010). To some extent spectroscopic measures of the velocity dispersions of a ...

The Astrophysical Journal, 2011

We present our results on the structure and activity of massive galaxies at z = 1 − 3 using one o... more We present our results on the structure and activity of massive galaxies at z = 1 − 3 using one of the largest (166 with M ⋆ ≥ 5 × 10 10 M ⊙ ) and most diverse samples of massive galaxies derived from the GOODS-NICMOS survey: (1) Sérsic fits to deep NIC3/F160W images indicate that the rest-frame optical structures of massive galaxies are very different at z = 2 − 3 compared to z ∼ 0. Approximately 40% of massive galaxies are ultra-compact (r e ≤ 2 kpc), compared to less than 1% at z ∼ 0. Furthermore, most (∼ 65%) systems at z = 2 − 3 have a low Sérsic index n ≤ 2, compared to ∼ 13% at z ∼ 0. We present evidence that the n ≤ 2 systems at z = 2 − 3 likely contain prominent disks, unlike most massive z ∼ 0 systems. There is a correlation between structure and star formation rates (SFR). The majority (∼ 85%) of non-AGN massive galaxies at z = 2 − 3, with SFR high enough to yield a 5σ (30µJy) 24 µm Spitzer detection have low n ≤ 2. Such n ≤ 2 systems host the highest SFR. The frequency of AGN is ∼ 40% at z = 2 − 3. Most (∼ 65%) AGN hosts have disky (n ≤ 2) morphologies. Ultra-compact galaxies appear quiescent in terms of both AGN activity and star formation. (4) Large stellar surface densities imply massive galaxies at z = 2 − 3 formed via rapid, highly dissipative events at z > 2. The large fraction of n ≤ 2 disky systems suggests cold mode accretion complements gas-rich major mergers at z > 2. In order for massive galaxies at z = 2 − 3 to evolve into present-day massive E/S0s, they need to significantly increase (n, r e ). Dry minor and major mergers may play an important role in this process.

Monthly Notices of the Royal Astronomical Society, 2011

We use a sample of 8298 galaxies observed as part of the HST H 160 -band GOODS NICMOS Survey (GNS... more We use a sample of 8298 galaxies observed as part of the HST H 160 -band GOODS NICMOS Survey (GNS) to construct the galaxy stellar mass function both as a function of redshift and stellar mass up to z = 3.5. Our mass functions are constructed within the redshift range z = 1 − 3.5 and consist of galaxies with stellar masses of M * = 10 12 M ⊙ down to nearly dwarf galaxy masses of M * = 10 8.5 M ⊙ in the lowest redshift bin. We discover that a significant fraction of all massive M * > 10 11 M ⊙ galaxies are in place up to the highest redshifts we probe, with a decreasing fraction of lower mass galaxies present at all redshifts. This is an example of 'galaxy mass downsizing', and is the result of massive galaxies forming before lower mass ones, and not just simply ending their star formation earlier as in traditional downsizing scenarios, whose effect is seen at z < 1.5. By fitting Schechter functions to our mass functions we find that the faint end slope ranges from α = −1.36 to −1.73, which is significantly steeper than what is found in previous investigations of the mass function at high redshift. We demonstrate that this steeper mass function better matches the stellar mass added due to star formation, thereby alleviating some of the mismatch between these two measures of the evolution of galaxy mass. We furthermore examine the stellar mass function divided into blue/red systems, as well as for star forming and non-star forming galaxies. We find a similar mass downsizing present for both blue/red and star-forming/non-star forming galaxies, and further find that red galaxies dominate at the high mass end of the mass function, but that the low mass galaxies are mostly all blue, and therefore blue galaxies are creating the steep mass functions observed at z > 2. We furthermore show that, although there is a downsizing such that high mass galaxies are nearer their z = 0 values at high redshift, this turns over at masses M * ∼ 10 10 M ⊙ , such that the lowest mass galaxies are more common than galaxies at slight higher masses, creating a 'dip' in the observed galaxy mass function. We argue that the galaxy assembly process may be driven by different mechanisms at low and high masses, and that the efficiency of the galaxy formation process is lowest at masses M * ∼ 10 10 M ⊙ at 1 < z < 3. Finally, we calculate the integrated stellar mass density for the total, blue and red populations. We find the integrated stellar mass density of the total and blue galaxy population is consistent with being constant over z = 1 − 2, while the red population shows an increase in integrated stellar mass density over the same redshift range.

Monthly Notices of the Royal Astronomical Society, 2014

We investigate the relationship between colour and structure within galaxies using a large, volum... more We investigate the relationship between colour and structure within galaxies using a large, volume-limited sample of bright, low-redshift galaxies with optical-near-infrared imaging from the GAMA survey. We fit single-component, wavelength-dependent, elliptical Sérsic models to all passbands simultaneously, using software developed by the MegaMorph project. Dividing our sample by n and colour, the recovered wavelength variations in effective radius (R e ) and Sérsic index (n) reveal the internal structure, and hence formation history, of different types of galaxies. All these trends depend on n; some have an additional dependence on galaxy colour. Late-type galaxies (n r < 2.5) show a dramatic increase in Sérsic index with wavelength. This might be a result of their two-component (bulge-disk) nature, though stellar population gradients within each component and dust attenuation are likely to play a role. All galaxies show a substantial decrease in R e with wavelength. This is strongest for early-types (n r > 2.5), even though they maintain constant n with wavelength, revealing that ellipticals are a superimposition of different stellar populations associated with multiple collapse and merging events. Processes leading to structures with larger R e must be associated with lower metallicity or younger stellar populations. This appears to rule out the formation of young cores through dissipative gas accretion as an important mechanism in the recent lives of luminous elliptical galaxies.

Monthly Notices of the Royal Astronomical Society, 2011

We investigate the relation between star formation rates and local galaxy environment for a stell... more We investigate the relation between star formation rates and local galaxy environment for a stellar mass selected galaxy sample in the redshift range 1.5 ≤ z ≤ 3. We use near-infra-red imaging from an extremely deep Hubble Space Telescope survey, the GOODS-NICMOS Survey (GNS) to measure local galaxy densities based on the nearest neighbour approach, while star-formation rates are estimated from rest-frame UV-fluxes. Due to our imaging depth we can examine galaxies down to a colour-independent stellar mass completeness limit of log M * = 9.5 M ⊙ at z ∼ 3. We find a strong dependence of star formation activity on galaxy stellar mass over the whole redshift range, which does not depend on local environment. The average star formation rates are largely independent of local environment apart from in the highest relative over-densities. Galaxies in over-densities of a factor of > 5 have on average lower star formation rates by a factor of 2 − 3, but only up to redshifts of z ∼ 2. We do not see any evidence for AGN activity influencing these relations. We also investigate the influence of the very local environment on star-formation activity by counting neighbours within 30 kpc radius. This shows that galaxies with two or more close neighbours have on average significantly lower star formation rates as well as lower specific star formation rates up to z ∼ 2.5. We suggest that this might be due to star formation quenching induced by galaxy merging processes.

Monthly Notices of the Royal Astronomical Society, 2012

We demonstrate a novel technology that combines the power of the multi-object spectrograph with t... more We demonstrate a novel technology that combines the power of the multi-object spectrograph with the spatial multiplex advantage of an integral field spectrograph (IFS). The Sydney-AAO Multi-object IFS (SAMI) is a prototype wide-field system at the Anglo-Australian Telescope (AAT) that allows 13 imaging fibre bundles ("hexabundles") to be deployed over a 1-degree diameter field of view. Each hexabundle comprises 61 lightly-fused multimode fibres with reduced cladding and yields a 75 percent filling factor. Each fibre core diameter subtends 1.6 arcseconds on the sky and each hexabundle has a field of view of 15 arcseconds diameter. The fibres are fed to the flexible AAOmega double-beam spectrograph, which can be used at a range of spectral resolutions (R = λ/δλ ≈ 1700-13000) over the optical spectrum (3700-9500Å). We present the first spectroscopic results obtained with SAMI for a sample of galaxies at z ≈ 0.05. We discuss the prospects of implementing hexabundles at a much higher multiplex over wider fields of view in order to carry out spatially-resolved spectroscopic surveys of 10 4 − 10 5 galaxies.

Monthly Notices of the Royal Astronomical Society, 2011

We present the details and early results from a deep near-Infrared survey utilising the NICMOS in... more We present the details and early results from a deep near-Infrared survey utilising the NICMOS instrument on the Hubble Space Telescope centred around massive M * > 10 11 M ⊙ galaxies at 1.7 < z < 2.9 found within the Great Observatories Origins Deep Survey (GOODS) fields North and South. The GOODS NICMOS Survey (GNS) was designed to obtain deep F160W (H-band) imaging of 80 of these massive galaxies, as well as other colour selected objects such as Lyman-break drop-outs, BzK objects, Distant Red Galaxies (DRGs), Extremely Red Objects (EROs), Spitzer Selected EROs, BX/BM galaxies, as well as flux selected sub-mm galaxies. We present in this paper details of the observations, our sample selection, as well as a description of features of the massive galaxies found within our survey fields. This includes: photometric redshifts, rest-frame colours, and stellar masses. We furthermore provide an analysis of the selection methods for finding massive galaxies at high redshifts, including colour selection methods and how galaxy populations selected through these colour methods overlap. We find that a single colour selection method cannot locate all of the massive galaxies, with no one method finding more than 70 percent. We however find that the combination of these colour methods finds nearly all the massive galaxies, as selected by photometric redshifts with the exception of apparently rare blue massive galaxies. By investigating the rest-frame (U − B) vs. M B diagram for these galaxies we furthermore show that there exists a bimodality in colour-magnitude space at z < 2, driven by stellar mass, such that the most massive galaxies are systematically red up to z ∼ 2.5, while lower mass galaxies tend to be blue. We also discuss the number densities for galaxies with stellar masses M * > 10 11 M ⊙ , whereby we find an increase of a factor of eight between z = 3 and z = 1.5, demonstrating that this is an epoch when massive galaxies establish most of their mass. We also provide an overview of the evolutionary properties of these galaxies, such as their merger histories, and size evolution.

Monthly Notices of the Royal Astronomical Society, 2011

We study the relationship between galaxy colour, stellar mass and local galaxy density in a deep ... more We study the relationship between galaxy colour, stellar mass and local galaxy density in a deep near-infrared imaging survey up to a redshift of z˜ 3 using the GOODS (Great Observatories Origins Deep Survey) NICMOS (Near Infrared Camera and Multi-Object Spectrometer) Survey (GNS). The GNS is a deep near-infrared Hubble Space Telescope survey imaging a total of 45 arcmin2 of

Monthly Notices of the Royal Astronomical Society, 2012

We present the results of an extended narrow-band Hα study of the massive galaxy cluster XMMU J22... more We present the results of an extended narrow-band Hα study of the massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. This paper represents a follow up study to our previous investigation of star-formation in the cluster centre, extending our analysis out to a projected cluster radius of 1.5 Mpc. Using the Near InfraRed Imager and Spectrograph (NIRI) on Gemini North we obtained deep H narrow-band imaging corresponding to the rest-frame wavelength of Hα at the cluster's redshift. We identify a total of 163 potential cluster members in both pointings, excluding stars based on their near-IR colours derived from VLT/HAWK-I imaging. Of these 163 objects 14 are spectroscopically confirmed cluster members, and 20% are excess line-emitters. We find no evidence of star formation activity within a radius of 200 kpc of the brightest cluster galaxy in the cluster core. Dust-corrected star formation rates (SFR) of excess emitters outside this cluster quenching radius, R Q ∼ 200 kpc, are on average = 2.7 ± 1.0 M ⊙ yr −1 , but do not show evidence of increasing star-formation rates toward the extreme 1.5 Mpc radius of the cluster. No individual cluster galaxy exceeds an SFR of 6 M ⊙ yr −1 . Massive galaxies (log M * /M ⊙ > 10.75) all have low specific SFRs (SSFRs, i.e. SFR per unit stellar mass). At fixed stellar mass, galaxies in the cluster centre have lower SSFRs than the rest of the cluster galaxies, which in turn have lower SSFRs than field galaxies at the same redshift by a factor of a few to 10. For the first time we can demonstrate through measurements of individual SFRs that already at very early epochs (at an age of the Universe of ∼4.5 Gyr) the suppression of star-formation is an effect of the cluster environment which persists at fixed galaxy stellar mass.

Monthly Notices of the Royal Astronomical Society, 2011

We present the first results of a narrow-band photometric study of the massive galaxy cluster XMM... more We present the first results of a narrow-band photometric study of the massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. We obtained deep H narrow-band imaging with NIRI on Gemini North, corresponding to Hα emission at the cluster's redshift. Our sample consists of 82 galaxies within a radius of ∼500 kpc, ten of which are spectroscopically confirmed cluster members. Sixteen galaxies are identified as excess line-emitters. Among just the excess line-emitting galaxies we find an average SFR of 3.6 ± 1.3 M ⊙ yr −1 . For spectroscopically confirmed cluster members we find a correlation between H broad-band magnitude and SFR such that brighter galaxies have lower SFRs. The probability that SFR and magnitude of confirmed members are uncorrelated is 0.7%. We also find a correlation between SFR and distance from the cluster centre for both confirmed and excess line-emitting candidate members, with a probability of 5% for there to be no correlation among confirmed members. All excess line-emitting candidate cluster members are located outside a radius of 200 kpc. We conclude that star formation is effectively shut off within the central 200 kpc radius (R QUEN CH ∼ 200 kpc) of this massive galaxy cluster at z = 1.39, when the universe was only 4.5 Gyr old.

Monthly Notices of the Royal Astronomical Society, 2011

... 4 AE Bauer et al. 2.3 Stellar masses and rest-frame colour Stellar masses and rest-frame colo... more ... 4 AE Bauer et al. 2.3 Stellar masses and rest-frame colour Stellar masses and rest-frame colours are determined from multi-colour stellar population fitting techniques using the same catalogue of five broad-band data points used to determine photometric red-shifts for all GNS ...

Arxiv preprint arXiv: …, 2011

Abstract: Here we report on the Women in Astronomy Workshop (this http URL), which was held on 13... more Abstract: Here we report on the Women in Astronomy Workshop (this http URL), which was held on 13 May 2011 in Sydney, Australia. The workshop was organised by the Astronomical Society of Australia's Chapter on Women in Astronomy, to discuss some of ...

Page 1. Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 4 April 2012 (MN LATEX style file v... more Page 1. Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 4 April 2012 (MN LATEX style file v2.2) Linking Star Formation Histories and Stellar Mass Growth in the GAMA Survey Amanda E. Bauer,1⋆ Andrew M. Hopkins ...

We present a study of the star formation rates for GOODS NICMOS Survey (GNS) galaxies, based on d... more We present a study of the star formation rates for GOODS NICMOS Survey (GNS) galaxies, based on deep HST/NICMOS H-band images of the GOODS North and South fields. We investigate the properties of 80 massive galaxies, with M*&amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;1011 Msun between 1.5&amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;z&amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;3. Utilizing the HST/ACS photometry of the massive galaxies, we calculate redshifts, stellar masses, star-forming properties, sizes, and morphologies to

The GOODS NICMOS Survey is a large Hubble Space Telescope programme to obtain deep H-band and J-b... more The GOODS NICMOS Survey is a large Hubble Space Telescope programme to obtain deep H-band and J-band imaging over the GOODS-North and South fields. The total exposure time is 180 orbits within the F160W filter (H-band) in fields surrounding massive galaxies with log M>11 at 2>z<3. This survey covers 1/3 of a GOODS field, and reaches a depth of H

We present a study of the relationship between galaxy colour, stellar mass, and local galaxy dens... more We present a study of the relationship between galaxy colour, stellar mass, and local galaxy density in a deep near-infrared imaging survey up to a redshift of z~3 using the GOODS NICMOS Survey (GNS). The GNS is a very deep, near-infrared Hubble Space Telescope survey imaging a total of 45 arcmin^2 in the GOODS fields, reaching a stellar mass completeness

Monthly Notices of the Royal Astronomical Society, 2015

We present the GAMA Panchromatic Data Release (PDR) constituting over 230deg 2 of imaging with ph... more We present the GAMA Panchromatic Data Release (PDR) constituting over 230deg 2 of imaging with photometry in 21 bands extending from the far-UV to the far-IR. These data complement our spectroscopic campaign of over 300k galaxies, and are compiled from observations with a variety of facilities including: GALEX, SDSS, VISTA, WISE, and Herschel, with the GAMA regions currently being surveyed by VST and scheduled for observations by ASKAP. These data are processed to a common astrometric solution, from which photometry is derived for ∼ 221, 373 galaxies with r < 19.8 mag. Online tools are provided to access and download data cutouts, or the full mosaics of the GAMA regions in each band.

Multiwavelength AGN Surveys - Proceedings of the Guillermo Haro Conference 2003, 2004

The Universe became fully reionized, and observable optically, at a time corresponding to redshif... more The Universe became fully reionized, and observable optically, at a time corresponding to redshift z ∼ 6.5, so it is only by studying the HI and molecular absorption lines against higher-redshift, radio-loud sources that one can hope to make detailed studies of the earliest stages of galaxy formation. At present no targets for such studies are known. In these proceedings we describe a survey which is underway to find radio-loud quasars at z > 6.5, and present broad-band SEDs of our most promising candidates.

Ground-based and Airborne Instrumentation for Astronomy IV, 2012

SAMI (Sydney-AAO Multi-object Integral field spectrograph) has the potential to revolutionise our... more SAMI (Sydney-AAO Multi-object Integral field spectrograph) has the potential to revolutionise our understanding of galaxies, with spatially-resolved spectroscopy of large numbers of targets. It is the first on-sky application of innovative photonic imaging bundles called hexabundles, which will remove the aperture effects that have biased previous single-fibre multi-object astronomical surveys. The hexabundles have lightly-fused circular multi-mode cores with a covering fraction of ∼ 73%. The thirteen hexabundles in SAMI, each have 61 fibre cores, and feed into the AAOmega spectrograph at the Anglo-Australian Telescope (AAT). SAMI was installed at the AAT in July 2011 and the first commissioning results prove the effectiveness of hexabundles on sky. A galaxy survey of several thousand galaxies to z ∼ 0.1 will begin with SAMI in mid-2012.

The Astrophysical Journal, 2012

We present the first scientific results from the Sydney-AAO Multi-Object IFS (SAMI) at the Anglo-... more We present the first scientific results from the Sydney-AAO Multi-Object IFS (SAMI) at the Anglo-Australian Telescope. This unique instrument deploys 13 fused fibre bundles (hexabundles) across a one-degree field of view allowing simultaneous spatially-resolved spectroscopy of 13 galaxies. During the first SAMI commissioning run, targeting a single galaxy field, one object (ESO 185-G031) was found to have extended minor axis emission with ionisation and kinematic properties consistent with a large-scale galactic wind. The importance of this result is two-fold: (i) fibre bundle spectrographs are able to identify low-surface brightness emission arising from extranuclear activity; (ii) such activity may be more common than presently assumed because conventional multi-object spectrographs use single-aperture fibres and spectra from these are nearly always dominated by nuclear emission. These early results demonstrate the extraordinary potential of multi-object hexabundle spectroscopy in future galaxy surveys.

The Astrophysical Journal, 2012

... up stellar matter in their outer regions (see, eg, Trujillo et al. 2007; Buitrago et al. 2008... more ... up stellar matter in their outer regions (see, eg, Trujillo et al. 2007; Buitrago et al. 2008; Cimatti et al. 2008; van Dokkum et al. 2009; Carrasco et al. 2010). To some extent spectroscopic measures of the velocity dispersions of a ...

The Astrophysical Journal, 2011

We present our results on the structure and activity of massive galaxies at z = 1 − 3 using one o... more We present our results on the structure and activity of massive galaxies at z = 1 − 3 using one of the largest (166 with M ⋆ ≥ 5 × 10 10 M ⊙ ) and most diverse samples of massive galaxies derived from the GOODS-NICMOS survey: (1) Sérsic fits to deep NIC3/F160W images indicate that the rest-frame optical structures of massive galaxies are very different at z = 2 − 3 compared to z ∼ 0. Approximately 40% of massive galaxies are ultra-compact (r e ≤ 2 kpc), compared to less than 1% at z ∼ 0. Furthermore, most (∼ 65%) systems at z = 2 − 3 have a low Sérsic index n ≤ 2, compared to ∼ 13% at z ∼ 0. We present evidence that the n ≤ 2 systems at z = 2 − 3 likely contain prominent disks, unlike most massive z ∼ 0 systems. There is a correlation between structure and star formation rates (SFR). The majority (∼ 85%) of non-AGN massive galaxies at z = 2 − 3, with SFR high enough to yield a 5σ (30µJy) 24 µm Spitzer detection have low n ≤ 2. Such n ≤ 2 systems host the highest SFR. The frequency of AGN is ∼ 40% at z = 2 − 3. Most (∼ 65%) AGN hosts have disky (n ≤ 2) morphologies. Ultra-compact galaxies appear quiescent in terms of both AGN activity and star formation. (4) Large stellar surface densities imply massive galaxies at z = 2 − 3 formed via rapid, highly dissipative events at z > 2. The large fraction of n ≤ 2 disky systems suggests cold mode accretion complements gas-rich major mergers at z > 2. In order for massive galaxies at z = 2 − 3 to evolve into present-day massive E/S0s, they need to significantly increase (n, r e ). Dry minor and major mergers may play an important role in this process.

Monthly Notices of the Royal Astronomical Society, 2011

We use a sample of 8298 galaxies observed as part of the HST H 160 -band GOODS NICMOS Survey (GNS... more We use a sample of 8298 galaxies observed as part of the HST H 160 -band GOODS NICMOS Survey (GNS) to construct the galaxy stellar mass function both as a function of redshift and stellar mass up to z = 3.5. Our mass functions are constructed within the redshift range z = 1 − 3.5 and consist of galaxies with stellar masses of M * = 10 12 M ⊙ down to nearly dwarf galaxy masses of M * = 10 8.5 M ⊙ in the lowest redshift bin. We discover that a significant fraction of all massive M * > 10 11 M ⊙ galaxies are in place up to the highest redshifts we probe, with a decreasing fraction of lower mass galaxies present at all redshifts. This is an example of 'galaxy mass downsizing', and is the result of massive galaxies forming before lower mass ones, and not just simply ending their star formation earlier as in traditional downsizing scenarios, whose effect is seen at z < 1.5. By fitting Schechter functions to our mass functions we find that the faint end slope ranges from α = −1.36 to −1.73, which is significantly steeper than what is found in previous investigations of the mass function at high redshift. We demonstrate that this steeper mass function better matches the stellar mass added due to star formation, thereby alleviating some of the mismatch between these two measures of the evolution of galaxy mass. We furthermore examine the stellar mass function divided into blue/red systems, as well as for star forming and non-star forming galaxies. We find a similar mass downsizing present for both blue/red and star-forming/non-star forming galaxies, and further find that red galaxies dominate at the high mass end of the mass function, but that the low mass galaxies are mostly all blue, and therefore blue galaxies are creating the steep mass functions observed at z > 2. We furthermore show that, although there is a downsizing such that high mass galaxies are nearer their z = 0 values at high redshift, this turns over at masses M * ∼ 10 10 M ⊙ , such that the lowest mass galaxies are more common than galaxies at slight higher masses, creating a 'dip' in the observed galaxy mass function. We argue that the galaxy assembly process may be driven by different mechanisms at low and high masses, and that the efficiency of the galaxy formation process is lowest at masses M * ∼ 10 10 M ⊙ at 1 < z < 3. Finally, we calculate the integrated stellar mass density for the total, blue and red populations. We find the integrated stellar mass density of the total and blue galaxy population is consistent with being constant over z = 1 − 2, while the red population shows an increase in integrated stellar mass density over the same redshift range.

Monthly Notices of the Royal Astronomical Society, 2014

We investigate the relationship between colour and structure within galaxies using a large, volum... more We investigate the relationship between colour and structure within galaxies using a large, volume-limited sample of bright, low-redshift galaxies with optical-near-infrared imaging from the GAMA survey. We fit single-component, wavelength-dependent, elliptical Sérsic models to all passbands simultaneously, using software developed by the MegaMorph project. Dividing our sample by n and colour, the recovered wavelength variations in effective radius (R e ) and Sérsic index (n) reveal the internal structure, and hence formation history, of different types of galaxies. All these trends depend on n; some have an additional dependence on galaxy colour. Late-type galaxies (n r < 2.5) show a dramatic increase in Sérsic index with wavelength. This might be a result of their two-component (bulge-disk) nature, though stellar population gradients within each component and dust attenuation are likely to play a role. All galaxies show a substantial decrease in R e with wavelength. This is strongest for early-types (n r > 2.5), even though they maintain constant n with wavelength, revealing that ellipticals are a superimposition of different stellar populations associated with multiple collapse and merging events. Processes leading to structures with larger R e must be associated with lower metallicity or younger stellar populations. This appears to rule out the formation of young cores through dissipative gas accretion as an important mechanism in the recent lives of luminous elliptical galaxies.

Monthly Notices of the Royal Astronomical Society, 2011

We investigate the relation between star formation rates and local galaxy environment for a stell... more We investigate the relation between star formation rates and local galaxy environment for a stellar mass selected galaxy sample in the redshift range 1.5 ≤ z ≤ 3. We use near-infra-red imaging from an extremely deep Hubble Space Telescope survey, the GOODS-NICMOS Survey (GNS) to measure local galaxy densities based on the nearest neighbour approach, while star-formation rates are estimated from rest-frame UV-fluxes. Due to our imaging depth we can examine galaxies down to a colour-independent stellar mass completeness limit of log M * = 9.5 M ⊙ at z ∼ 3. We find a strong dependence of star formation activity on galaxy stellar mass over the whole redshift range, which does not depend on local environment. The average star formation rates are largely independent of local environment apart from in the highest relative over-densities. Galaxies in over-densities of a factor of > 5 have on average lower star formation rates by a factor of 2 − 3, but only up to redshifts of z ∼ 2. We do not see any evidence for AGN activity influencing these relations. We also investigate the influence of the very local environment on star-formation activity by counting neighbours within 30 kpc radius. This shows that galaxies with two or more close neighbours have on average significantly lower star formation rates as well as lower specific star formation rates up to z ∼ 2.5. We suggest that this might be due to star formation quenching induced by galaxy merging processes.

Monthly Notices of the Royal Astronomical Society, 2012

We demonstrate a novel technology that combines the power of the multi-object spectrograph with t... more We demonstrate a novel technology that combines the power of the multi-object spectrograph with the spatial multiplex advantage of an integral field spectrograph (IFS). The Sydney-AAO Multi-object IFS (SAMI) is a prototype wide-field system at the Anglo-Australian Telescope (AAT) that allows 13 imaging fibre bundles ("hexabundles") to be deployed over a 1-degree diameter field of view. Each hexabundle comprises 61 lightly-fused multimode fibres with reduced cladding and yields a 75 percent filling factor. Each fibre core diameter subtends 1.6 arcseconds on the sky and each hexabundle has a field of view of 15 arcseconds diameter. The fibres are fed to the flexible AAOmega double-beam spectrograph, which can be used at a range of spectral resolutions (R = λ/δλ ≈ 1700-13000) over the optical spectrum (3700-9500Å). We present the first spectroscopic results obtained with SAMI for a sample of galaxies at z ≈ 0.05. We discuss the prospects of implementing hexabundles at a much higher multiplex over wider fields of view in order to carry out spatially-resolved spectroscopic surveys of 10 4 − 10 5 galaxies.

Monthly Notices of the Royal Astronomical Society, 2011

We present the details and early results from a deep near-Infrared survey utilising the NICMOS in... more We present the details and early results from a deep near-Infrared survey utilising the NICMOS instrument on the Hubble Space Telescope centred around massive M * > 10 11 M ⊙ galaxies at 1.7 < z < 2.9 found within the Great Observatories Origins Deep Survey (GOODS) fields North and South. The GOODS NICMOS Survey (GNS) was designed to obtain deep F160W (H-band) imaging of 80 of these massive galaxies, as well as other colour selected objects such as Lyman-break drop-outs, BzK objects, Distant Red Galaxies (DRGs), Extremely Red Objects (EROs), Spitzer Selected EROs, BX/BM galaxies, as well as flux selected sub-mm galaxies. We present in this paper details of the observations, our sample selection, as well as a description of features of the massive galaxies found within our survey fields. This includes: photometric redshifts, rest-frame colours, and stellar masses. We furthermore provide an analysis of the selection methods for finding massive galaxies at high redshifts, including colour selection methods and how galaxy populations selected through these colour methods overlap. We find that a single colour selection method cannot locate all of the massive galaxies, with no one method finding more than 70 percent. We however find that the combination of these colour methods finds nearly all the massive galaxies, as selected by photometric redshifts with the exception of apparently rare blue massive galaxies. By investigating the rest-frame (U − B) vs. M B diagram for these galaxies we furthermore show that there exists a bimodality in colour-magnitude space at z < 2, driven by stellar mass, such that the most massive galaxies are systematically red up to z ∼ 2.5, while lower mass galaxies tend to be blue. We also discuss the number densities for galaxies with stellar masses M * > 10 11 M ⊙ , whereby we find an increase of a factor of eight between z = 3 and z = 1.5, demonstrating that this is an epoch when massive galaxies establish most of their mass. We also provide an overview of the evolutionary properties of these galaxies, such as their merger histories, and size evolution.

Monthly Notices of the Royal Astronomical Society, 2011

We study the relationship between galaxy colour, stellar mass and local galaxy density in a deep ... more We study the relationship between galaxy colour, stellar mass and local galaxy density in a deep near-infrared imaging survey up to a redshift of z˜ 3 using the GOODS (Great Observatories Origins Deep Survey) NICMOS (Near Infrared Camera and Multi-Object Spectrometer) Survey (GNS). The GNS is a deep near-infrared Hubble Space Telescope survey imaging a total of 45 arcmin2 of

Monthly Notices of the Royal Astronomical Society, 2012

We present the results of an extended narrow-band Hα study of the massive galaxy cluster XMMU J22... more We present the results of an extended narrow-band Hα study of the massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. This paper represents a follow up study to our previous investigation of star-formation in the cluster centre, extending our analysis out to a projected cluster radius of 1.5 Mpc. Using the Near InfraRed Imager and Spectrograph (NIRI) on Gemini North we obtained deep H narrow-band imaging corresponding to the rest-frame wavelength of Hα at the cluster's redshift. We identify a total of 163 potential cluster members in both pointings, excluding stars based on their near-IR colours derived from VLT/HAWK-I imaging. Of these 163 objects 14 are spectroscopically confirmed cluster members, and 20% are excess line-emitters. We find no evidence of star formation activity within a radius of 200 kpc of the brightest cluster galaxy in the cluster core. Dust-corrected star formation rates (SFR) of excess emitters outside this cluster quenching radius, R Q ∼ 200 kpc, are on average = 2.7 ± 1.0 M ⊙ yr −1 , but do not show evidence of increasing star-formation rates toward the extreme 1.5 Mpc radius of the cluster. No individual cluster galaxy exceeds an SFR of 6 M ⊙ yr −1 . Massive galaxies (log M * /M ⊙ > 10.75) all have low specific SFRs (SSFRs, i.e. SFR per unit stellar mass). At fixed stellar mass, galaxies in the cluster centre have lower SSFRs than the rest of the cluster galaxies, which in turn have lower SSFRs than field galaxies at the same redshift by a factor of a few to 10. For the first time we can demonstrate through measurements of individual SFRs that already at very early epochs (at an age of the Universe of ∼4.5 Gyr) the suppression of star-formation is an effect of the cluster environment which persists at fixed galaxy stellar mass.

Monthly Notices of the Royal Astronomical Society, 2011

We present the first results of a narrow-band photometric study of the massive galaxy cluster XMM... more We present the first results of a narrow-band photometric study of the massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. We obtained deep H narrow-band imaging with NIRI on Gemini North, corresponding to Hα emission at the cluster's redshift. Our sample consists of 82 galaxies within a radius of ∼500 kpc, ten of which are spectroscopically confirmed cluster members. Sixteen galaxies are identified as excess line-emitters. Among just the excess line-emitting galaxies we find an average SFR of 3.6 ± 1.3 M ⊙ yr −1 . For spectroscopically confirmed cluster members we find a correlation between H broad-band magnitude and SFR such that brighter galaxies have lower SFRs. The probability that SFR and magnitude of confirmed members are uncorrelated is 0.7%. We also find a correlation between SFR and distance from the cluster centre for both confirmed and excess line-emitting candidate members, with a probability of 5% for there to be no correlation among confirmed members. All excess line-emitting candidate cluster members are located outside a radius of 200 kpc. We conclude that star formation is effectively shut off within the central 200 kpc radius (R QUEN CH ∼ 200 kpc) of this massive galaxy cluster at z = 1.39, when the universe was only 4.5 Gyr old.

Monthly Notices of the Royal Astronomical Society, 2011

... 4 AE Bauer et al. 2.3 Stellar masses and rest-frame colour Stellar masses and rest-frame colo... more ... 4 AE Bauer et al. 2.3 Stellar masses and rest-frame colour Stellar masses and rest-frame colours are determined from multi-colour stellar population fitting techniques using the same catalogue of five broad-band data points used to determine photometric red-shifts for all GNS ...

Arxiv preprint arXiv: …, 2011

Abstract: Here we report on the Women in Astronomy Workshop (this http URL), which was held on 13... more Abstract: Here we report on the Women in Astronomy Workshop (this http URL), which was held on 13 May 2011 in Sydney, Australia. The workshop was organised by the Astronomical Society of Australia's Chapter on Women in Astronomy, to discuss some of ...

Page 1. Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 4 April 2012 (MN LATEX style file v... more Page 1. Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 4 April 2012 (MN LATEX style file v2.2) Linking Star Formation Histories and Stellar Mass Growth in the GAMA Survey Amanda E. Bauer,1⋆ Andrew M. Hopkins ...

We present a study of the star formation rates for GOODS NICMOS Survey (GNS) galaxies, based on d... more We present a study of the star formation rates for GOODS NICMOS Survey (GNS) galaxies, based on deep HST/NICMOS H-band images of the GOODS North and South fields. We investigate the properties of 80 massive galaxies, with M*&amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;1011 Msun between 1.5&amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;z&amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;3. Utilizing the HST/ACS photometry of the massive galaxies, we calculate redshifts, stellar masses, star-forming properties, sizes, and morphologies to