arXiv subjects

Jeffrey A. Rich

Publications and source records attributed to Jeffrey A. Rich.

At least 37 records · Page 2Linked to original sources

arXiv2018

The Carnegie-Chicago Hubble Program. IV. The Distances to NGC 4424, NGC 4526, and NGC 4536 via the Tip of the Red Giant Branch

The Carnegie-Chicago Hubble Program (CCHP) is undertaking a re-calibration of the extragalactic distance scale, using Type Ia supernovae that are tied to Tip of the Red Giant Branch (TRGB) distances to local galaxies. We present here deep Hubble Space Telescope (HST) ACS/WFC imaging of the resolved stellar populations in the metal-poor halos of the SN Ia host galaxies NGC 4424, NGC 4526, and NGC 4536. These three Virgo constellation galaxies are prime targets for calibrating the extragalactic distance scale given their relative proximity in the local Universe and their low line-of-sight reddenings. Anchoring the TRGB zero-point to the geometric distance to the Large Magellanic Cloud via detached eclipsing binaries, we measure extinction-corrected distance moduli of 31.00 +/- 0.03 (stat) +/- 0.06 (sys) mag, 30.98 +/- 0.03 (stat) +/- 0.06 (sys) mag, and 30.99 +/- 0.03 (stat) +/- 0.06 (sys) mag for NGC 4424, NGC 4526, and NGC 4536, respectively, or 15.8 +/- 0.2 (stat) +/- 0.4 (sys) Mpc, 15.7 +/- 0.2 (stat) +/- 0.4 (sys) Mpc, and 15.8 +/- 0.2 (stat) +/- 0.4 (sys) Mpc. For these three galaxies, the distances are the first based on the TRGB, and for NGC 4424 and NGC 4526, they are the highest precision distances published to date, each measured to 3%. Finally, we report good agreement between our TRGB distances and the available Cepheid distances for NGC 4424 and NGC 4536, demonstrating consistency between the distance scales currently derived from stars of Population I and II.

astro-ph.CO↗

arXiv2018

The Carnegie-Chicago Hubble Program. V. The Distances to NGC 1448 and NGC 1316 via the Tip of the Red Giant Branch

The Carnegie-Chicago Hubble Program (CCHP) is re-calibrating the extragalactic SN Ia distance scale using exclusively Population II stars. This effort focuses on the Tip of the Red Giant Branch (TRGB) method, whose systematics are entirely independent of the Population I Cepheid-based determinations that have long served as calibrators for the SN Ia distance scale. We present deep Hubble Space Telescope imaging of the low surface-density and low line-of-sight reddening halos of two galaxies, NGC 1448 and NGC 1316, each of which have been hosts to recent SN Ia events. Provisionally anchoring the TRGB zero-point to the geometric distance to the Large Magellanic Cloud derived from detached eclipsing binaries, we measure extinction-corrected distance moduli of 31.23 +/-0.04 (stat) +/- 0.06 (sys) mag for NGC 1448 and 31.37 +/- 0.04 (stat) and +/- 0.06 (sys) mag for NGC 1316, respectively, giving metric distances of 17.7 +/- 0.3 (stat) +/- 0.5 (sys) Mpc, and 18.8 +/- 0.3 (stat) +/- 0.5 (sys) Mpc. We find agreement between our result and the available Cepheid distance for NGC 1448; for NGC 1316, where there are relatively few published distances based on direct measurements, we find that our result is consistent with the published SN Ia distances whose absolute scales are set from other locally-determined methods such as Cepheids. For NGC 1448 and NGC 1316, our distances are some of the most precise (and systematically accurate) measurements with errors at 1.7 (2.8) % and 1.6 (2.7) % levels, respectively.

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arXiv2018

Shocked POststarburst Galaxy Survey. III. The Ultraviolet Properties of SPOGs

The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify galaxies in the transitional phase between actively star-forming and quiescence with nebular lines that are excited from shocks rather than star formation processes. We explored the ultraviolet (UV) properties of objects with near-ultraviolet (NUV) and far-ultraviolet (FUV) photometry from archival GALEX data; 444 objects were detected in both bands, 365 in only NUV, and 24 in only FUV, for a total of 833 observed objects. We compared SPOGs to samples of Star-forming galaxies (SFs), Quiescent galaxies (Qs), classical E+A post-starburst galaxies, active galactic nuclei (AGN) host galaxies, and interacting galaxies. We found that SPOGs have a larger range in their FUV-NUV and NUV-r colors compared to most of the other samples, although all of our comparison samples occupied color space inside of the SPOGs region. Based on their UV colors, SPOGs are a heterogeneous group, possibly made up of a mixture of SFs, Qs, and/or AGN. Using Gaussian mixture models, we are able to recreate the distribution of FUV-NUV colors of SPOGs and E+A galaxies with different combinations of SFs, Qs, and AGN. We find that the UV colors of SPOGs require a >60% contribution from SFs, with either Qs or AGN representing the remaining contribution, while UV colors of E+A galaxies required a significantly lower fraction of SFs, supporting the idea that SPOGs are at an earlier point in their transition from quiescent to star-forming than E+A galaxies.

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arXiv2018

Azimuthal variations of gas-phase oxygen abundance in NGC 2997

The azimuthal variation of the HII region oxygen abundance in spiral galaxies is a key observable for understanding how quickly oxygen produced by massive stars can be dispersed within the surrounding interstellar medium. Observational constraints on the prevalence and magnitude of such azimuthal variations remain rare in the literature. Here, we report the discovery of pronounced azimuthal variations of HII region oxygen abundance in NGC 2997, a spiral galaxy at approximately 11.3 Mpc. Using 3D spectroscopic data from the TYPHOON Program, we study the HII region oxygen abundance at a physical resolution of 125 pc. Individual HII regions or complexes are identified in the 3D optical data and their strong emission line fluxes measured to constrain their oxygen abundances. We find 0.06 dex azimuthal variations in the oxygen abundance on top of a radial abundance gradient that is comparable to those seen in other star-forming disks. At a given radial distance, the oxygen abundances are highest in the spiral arms and lower in the inter-arm regions, similar to what has been reported in NGC 1365 using similar observations. We discuss whether the azimuthal variations could be recovered when the galaxy is observed at worse physical resolutions and lower signal-to-noise ratios.

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arXiv2018

ASASSN-15nx: A luminous Type II supernova with a "perfect" linear decline

We report a luminous Type II supernova, ASASSN-15nx, with a peak luminosity of M_V=-20 mag, that is between typical core-collapse supernovae and super-luminous supernovae. The post-peak optical light curves show a long, linear decline with a steep slope of 2.5 mag/100 days (i.e., an exponential decline in flux), through the end of observations at phase ~260 days. In contrast, the light curves of hydrogen rich supernovae (SNe II-P/L) always show breaks in their light curves at phase ~100 days, before settling onto Co56 radioactive decay tails with a decline rate of about 1 mag/100 days. The spectra of ASASSN-15nx do not exhibit the narrow emission-line features characteristic of Type IIn SNe, which can have a wide variety of light-curve shapes usually attributed to strong interactions with a dense circumstellar medium (CSM). ASASSN-15nx has a number of spectroscopic peculiarities, including a relatively weak and triangularly-shaped H-alpha emission profile with no absorption component. The physical origin of these peculiarities is unclear, but the long and linear post-peak light curve without a break suggests a single dominant powering mechanism. Decay of a large amount of Ni56 (M_Ni56 = 1.6 +/- 0.2 M_sun) can power the light curve of ASASSN-15nx, and the steep light-curve slope requires substantial gamma-ray escape from the ejecta, which is possible given a low-mass hydrogen envelope for the progenitor. Another possibility is strong CSM interactions powering the light curve, but the CSM needs to be sculpted to produce the unique light-curve shape and to avoid producing SN IIn-like narrow emission lines.

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arXiv2018

The Near-Infrared Tip of the Red Giant Branch. II. An Absolute Calibration in the Large Magellanic Cloud

We present a new empirical $JHK$ absolute calibration of the tip of the red giant branch (TRGB) in the Large Magellanic Cloud (LMC). We use published data from the extensive \emph{Near-Infrared Synoptic Survey} containing 3.5 million stars, of which 65,000 are red giants that fall within one magnitude of the TRGB. Adopting the TRGB slopes from a companion study of the isolated dwarf galaxy IC\,1613 as well as an LMC distance modulus of $μ_0 = $~18.49~mag from (geometric) detached eclipsing binaries, we derive absolute $JHK$ zero-points for the near-infrared TRGB. For comparison with measurements in the bar alone, we apply the calibrated $JHK$ TRGB to a 500 deg\textsuperscript{2} area of the 2MASS survey. The TRGB reveals the 3-dimensional structure of the LMC with a tilt in the direction perpendicular to the major axis of the bar, in agreement with previous studies.

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arXiv2018

The Near-Infrared Tip of the Red Giant Branch. I. A Calibration in the Isolated Dwarf Galaxy IC 1613

Based on observations from the \emph{FourStar} near-infrared camera on the 6.5m Baade-Magellan telescope at Las Campanas, Chile, we present calibrations of the $JHK$ luminosities of stars defining the tip of the red giant branch (TRGB) in the halo of the Local Group dwarf galaxy IC 1613. We employ metallicity-independent (rectified) T-band magnitudes---constructed using $J,H$ and $K$-band magnitudes and both $(J-H)~ \& ~(J-K)$ colors in order to flatten the upward-sloping red giant branch tips as otherwise seen in their apparent color-magnitude diagrams. We describe and quantify the advantages of working at these particular near-infrared wavelengths, which are applicable to both \emph{HST} and \emph{JWST}. We also note that these same wavelengths can be accessed from the ground for an eventual tie-in to \emph{Gaia} for absolute astrometry and parallaxes to calibrate the intrinsic luminosity of the TRGB. Adopting the color terms derived from the IC 1613 data, as well as the zero-points from a companion study of the Large Magellanic Cloud whose distance is anchored to the geometric distances of detached eclipsing binaries, we find a true distance modulus of 24.32 $\pm$ 0.02~ (statistical) $\pm$ 0.06~mag (systematic) for IC 1613, which compares favorably with the recently published multi-wavelength, multi-method consensus modulus of 24.30 $\pm$ 0.05~mag by Hatt et al. (2017).

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arXiv2017

The Carnegie-Chicago Hubble Program. II. The Distance to IC 1613: The Tip of the Red Giant Branch and RR Lyrae Period-Luminosity Relations

IC 1613 is an isolated dwarf galaxy within the Local Group. Low foreground and internal extinction, low metallicity, and low crowding make it an invaluable testbed for the calibration of the local distance ladder. We present new, high-fidelity distance estimates to IC 1613 via its Tip of the Red Giant Branch (TRGB) and its RR Lyrae (RRL) variables as part of the Carnegie-Chicago Hubble Program, which seeks an alternate local route to \ho using Population II stars. We have measured a TRGB magnitude I=20.35+/-0.01 (statistical)+/-0.01 (systematic) using wide-field observations obtained from the IMACS camera on the Magellan-Baade telescope. We have further constructed optical and near-infrared RRL light curves using archival BI- and new H- band observations from the ACS/WFC and WFC3/IR instruments aboard the Hubble Space Telescope (HST). In advance of future Gaia data releases, we set provisional values for the TRGB luminosity via the Large Magellanic Cloud and Galactic RRL zero-points via HST parallaxes. We find corresponding true distance moduli μ(TRGB)=24.30+/-0.03 (statistical)+/-0.05 (systematic) and μ(RRL)=24.28+/-0.04 (statistical+systematic). We compare our results to a body of recent publications on IC 1613 and find no statistically significant difference between the distances derived from stars of Population I and II.

astro-ph.CO↗

arXiv2017

The Chemical Evolution Carousel of Spiral Galaxies: Azimuthal Variations of Oxygen Abundance in NGC1365

The spatial distribution of oxygen in the interstellar medium of galaxies is the key to understanding how efficiently metals that are synthesized in massive stars can be redistributed across a galaxy. We present here a case study in the nearby spiral galaxy NGC1365 using 3D optical data obtained in the TYPHOON Program. We find systematic azimuthal variations of the HII region oxygen abundance imprinted on a negative radial gradient. The 0.2 dex azimuthal variations occur over a wide radial range of 0.3 to 0.7 R25 and peak at the two spiral arms in NGC1365. We show that the azimuthal variations can be explained by two physical processes: gas undergoes localized, sub-kpc scale self-enrichment when orbiting in the inter-arm region, and experiences efficient, kpc scale mixing-induced dilution when spiral density waves pass through. We construct a simple chemical evolution model to quantitatively test this picture and find that our toy model can reproduce the observations. This result suggests that the observed abundance variations in NGC1365 are a snapshot of the dynamical local enrichment of oxygen modulated by spiral-driven, periodic mixing and dilution.

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arXiv2017

The Carnegie-Chicago Hubble Program. III. The Distance to NGC 1365 via the Tip of the Red Giant Branch

The Carnegie-Chicago Hubble Program seeks to anchor the distance scale of Type Ia supernovae via the Tip of the Red Giant Branch (TRGB). Based on deep $Hubble$ $Space$ $Telescope$ ACS/WFC imaging, we present an analysis of the TRGB for the metal-poor halo of NGC 1365, a giant spiral galaxy in the Fornax Cluster that is host to the supernova SN2012fr. We have measured its extinction-corrected TRGB magnitude to be F814W $= 27.34 \pm 0.03_{stat} \pm0.01_{sys}$ mag. In advance of future direct calibration by $Gaia$, we set a provisional TRGB luminosity via the Large Magellanic Cloud and find a true distance modulus $μ_0 = 31.29 \pm 0.04_{stat}\pm0.05_{sys}$ mag or $D = 18.1 \pm 0.3_{stat} \pm0.4_{sys}$ Mpc. This high-fidelity measurement shows excellent agreement with recent Cepheid-based distances to NGC 1365 and suggests no significant difference in the distances derived from stars of Population I and II. We revisit the error budget for the $CCHP$ path to the Hubble Constant based on this analysis of one of our most distant hosts, finding a 2.5% measurement is feasible with our current sample.

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arXiv2017

Standard Galactic Field RR Lyrae. I. Optical to Mid-infrared Phased Photometry

We present a multi-wavelength compilation of new and previously-published photometry for 55 Galactic field RR Lyrae variables. Individual studies, spanning a time baseline of up to 30 years, are self-consistently phased to produce light curves in 10 photometric bands covering the wavelength range from 0.4 to 4.5 microns. Data smoothing via the GLOESS technique is described and applied to generate high-fidelity light curves, from which mean magnitudes, amplitudes, rise-times, and times of minimum and maximum light are derived. 60,000 observations were acquired using the new robotic Three-hundred MilliMeter Telescope (TMMT), which was first deployed at the Carnegie Observatories in Pasadena, CA, and is now permanently installed and operating at Las Campanas Observatory in Chile. We provide a full description of the TMMT hardware, software, and data reduction pipeline. Archival photometry contributed approximately 31,000 observations. Photometric data are given in the standard Johnson UBV, Kron-Cousins RI, 2MASS JHK, and Spitzer [3.6] & [4.5] bandpasses.

astro-ph.SR↗

arXiv2016

The Carnegie-Chicago Hubble Program. I. An Independent Approach to the Extragalactic Distance Scale Using only Population II Distance Indicators

We present an overview of the Carnegie-Chicago Hubble Program, an ongoing program to obtain a 3 per cent measurement of the Hubble constant using alternative methods to the traditional Cepheid distance scale. We aim to establish a completely independent route to the Hubble constant using RR Lyrae variables, the tip of the red giant branch (TRGB), and Type Ia supernovae (SNe Ia). This alternative distance ladder can be applied to galaxies of any Hubble Type, of any inclination, and, utilizing old stars in low density environments, is robust to the degenerate effects of metallicity and interstellar extinction. Given the relatively small number of SNe Ia host galaxies with independently measured distances, these properties provide a great systematic advantage in the measurement of the Hubble constant via the distance ladder. Initially, the accuracy of our value of the Hubble constant will be set by the five Galactic RR Lyrae calibrators with Hubble Space Telescope Fine-Guidance Sensor parallaxes. With Gaia, both the RR Lyrae zero point and TRGB method will be independently calibrated, the former with at least an order of magnitude more calibrators and the latter directly through parallax measurement of tip red giants. As the first end-to-end "distance ladder" completely independent of both Cepheid variables and the Large Magellanic Cloud, this path to the Hubble constant will allow for the high precision comparison at each rung of the traditional distance ladder that is necessary to understand tensions between this and other routes to the Hubble constant.

astro-ph.CO↗

arXiv2016

Shocked POststarburst Galaxy Survey II: The Molecular Gas Content and Properties of a Subset of SPOGs

We present CO(1-0) observations of objects within the Shocked POststarburst Galaxy Survey taken with the Institut de Radioastronomie Millimetrique (IRAM) 30m single dish and the Combined Array for Research for Millimeter Astronomy (CARMA) interferometer. Shocked Poststarburst Galaxies (SPOGs) represent a transitioning population of galaxies, with deep Balmer absorption (Hdelta>5A), consistent with an intermediate-age (A-star) stellar population, and ionized gas line ratios inconsistent with pure star formation. The CO(1-0) subsample was selected from SPOGs detected by the Wide-field Infrared Survey Explorer with 22um flux detected at a signal-to-noise (S/N)>3. Of the 52 objects observed in CO(1-0), 47 are detected with S/N>3. A large fraction (37-46%) of our CO-SPOG sample were visually classified as morphologically disrupted. The H2 masses detected were between 10^(8.7-10.8) Msuns, consistent with the gas masses found in normal galaxies, though approximately an order of magnitude larger than the range seen in poststarburst galaxies. When comparing the 22um and CO(1-0) fluxes, SPOGs diverge from the normal star-forming relation, having 22um fluxes in excess by a factor of =4.91+0.42-0.39. The Na I D characteristics of CO-SPOGs show that it is likely that many of these objects host interstellar winds. Objects with the large Na I D enhancements also tend to emit in the radio, suggesting possible AGN-driving of neutral winds.

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arXiv2016

LZIFU: an emission-line fitting toolkit for integral field spectroscopy data

We present LZIFU (LaZy-IFU), an IDL toolkit for fitting multiple emission lines simultaneously in integral field spectroscopy (IFS) data. LZIFU is useful for the investigation of the dynamical, physical and chemical properties of gas in galaxies. LZIFU has already been applied to many world-class IFS instruments and large IFS surveys, including the Wide Field Spectrograph, the new Multi Unit Spectroscopic Explorer (MUSE), the Calar Alto Legacy Integral Field Area (CALIFA) survey, the Sydney-Australian-astronomical-observatory Multi-object Integral-field spectrograph (SAMI) Galaxy Survey. Here we describe in detail the structure of the toolkit, and how the line fluxes and flux uncertainties are determined, including the possibility of having multiple distinct kinematic components. We quantify the performance of LZIFU, demonstrating its accuracy and robustness. We also show examples of applying LZIFU to CALIFA and SAMI data to construct emission line and kinematic maps, and investigate complex, skewed line profiles presented in IFS data. The code is made available to the astronomy community through github. LZIFU will be further developed over time to other IFS instruments, and to provide even more accurate line and uncertainty estimates.

astro-ph.GA↗

arXiv2016

On the Classification of UGC1382 as a Giant Low Surface Brightness Galaxy

We provide evidence that UGC1382, long believed to be a passive elliptical galaxy, is actually a giant low surface brightness (GLSB) galaxy which rivals the archetypical GLSB Malin 1 in size. Like other GLSB galaxies, it has two components: a high surface brightness disk galaxy surrounded by an extended low surface brightness (LSB) disk. For UGC1382, the central component is a lenticular system with an effective radius of 6 kpc. Beyond this, the LSB disk has an effective radius of ~38 kpc and an extrapolated central surface brightness of ~26 mag/arcsec^2. Both components have a combined stellar mass of ~8x10^10 M_sun, and are embedded in a massive (10^10 M_sun) low-density (<3 M_sun/pc^2) HI disk with a radius of 110 kpc, making this one of the largest isolated disk galaxies known. The system resides in a massive dark matter halo of at least 2x10^12 M_sun. Although possibly part of a small group, its low density environment likely plays a role in the formation and retention of the giant LSB and HI disks. We model the spectral energy distributions and find that the LSB disk is likely older than the lenticular component. UGC1382 has UV-optical colors typical of galaxies transitioning through the green valley. Within the LSB disk are spiral arms forming stars at extremely low efficiencies. The gas depletion time scale of ~10^11 yr suggests that UGC1382 may be a very long term resident of the green valley. We find that the formation and evolution of the LSB disk is best explained by the accretion of gas-rich LSB dwarf galaxies.

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arXiv2016

Shocked POststarbust Galaxy Survey I: Candidate Poststarbust Galaxies with Emission Line Ratios Consistent with Shocks

[Abridged] The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify transforming galaxies, in which the nebular lines are excited via shocks instead of through star formation processes. Utilizing the OSSY measurements on the Sloan Digital Sky Survey Data Release 7 catalog, we applied Balmer absorption and shock boundary criteria to identify 1,067 SPOG candidates (SPOGs*) within z=0.2. SPOGs* represent 0.2% of the OSSY sample galaxies that exceed the continuum signal-to-noise cut (and 0.7% of the emission line galaxy sample). SPOGs* colors suggest that they are in an earlier phase of transition than OSSY galaxies that meet an E+A selection. SPOGs* have a 13% 1.4GHz detection rate from the Faint Images of the Radio Sky at Twenty centimeters survey, higher than most other subsamples, and comparable only to low-ionization nuclear emission line region hosts, suggestive of the presence of active galactic nuclei. SPOGs* also have stronger NaD absorption than predicted from the stellar population, suggestive of cool gas being driven out in galactic winds. It appears that SPOGs* represent an earlier phase in galaxy transformation than traditionally selected poststarburst galaxies, and that a large proportion of SPOGs* also have properties consistent with disruption of their interstellar media, a key component to galaxy transformation. It is likely that many of the known pathways to transformation undergo a SPOG phase. Studying this sample of SPOGs* further, including their morphologies, active galactic nuclei properties, and environments, has the potential for us to build a more complete picture of the initial conditions that can lead to a galaxy evolving.

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arXiv2016

The Carnegie Chicago Hubble Program: The Mid-Infrared Colours of Cepheids and the Effect of Metallicity on the CO Band-head at $4.6μ$m

We compare mid-infrared 3.6 and 4.5 $μ$m Warm Spitzer observations for Cepheids in the Milky Way and the Large and Small Magellanic Clouds. Using models, we explore in detail the effect of the CO rotation-vibration band-head at 4.6 $μ$m on the mid-infrared photometry. We confirm the temperature sensitivity of the CO band-head at 4.6 $μ$m and find no evidence for an effect at 3.6 $μ$m. We compare the ([3.6]-[4.5]) period-colour relations in the MW, LMC, and SMC. The slopes of the period-colour relations for the three galaxies are in good agreement, but there is a trend in zero-point with metallicity, with the lowest metallicity Cepheids having redder mid-IR colours. Finally, we present a colour-[Fe/H] relation based on published spectroscopic metallicities. This empirical relation, calibrated to the metallicity system of Genovali et al. (2014), demonstrates that the ([3.6]-[4.5]) colour provides a reliable metallicity indicator for Cepheids, with a precision comparable to current spectroscopic determinations.

astro-ph.SR↗

arXiv2015

Kinematic classifications of local interacting galaxies: implications for the merger/disk classifications at high-z

The classification of galaxy mergers and isolated disks is key for understanding the relative importance of galaxy interactions and secular evolution during the assembly of galaxies. The kinematic properties of galaxies as traced by emission lines have been used to suggest the existence of a significant population of high-z star-forming galaxies consistent with isolated rotating disks. However, recent studies have cautioned that post-coalescence mergers may also display disk-like kinematics. To further investigate the robustness of merger/disk classifications based on kinematic properties, we carry out a systematic classification of 24 local (U)LIRGs spanning a range of galaxy morphologies: from isolated spiral galaxies, ongoing interacting systems, to fully merged remnants. We artificially redshift the WiFeS observations of these local (U)LIRGs to z=1.5 to make a realistic comparison with observations at high-z, and also to ensure that all galaxies have the same spatial sampling of ~900 pc. Using both kinemetry-based and visual classifications, we find that the reliability of kinematic classification shows a strong trend with the interaction stage of galaxies. Mergers with two nuclei and tidal tails have the most distinct kinematic properties compared to isolated disks, whereas a significant population of the interacting disks and merger remnants are indistinguishable from isolated disks. The high fraction of late-stage mergers showing disk-like kinematics reflects the complexity of the dynamics during galaxy interactions. However, the exact fractions of misidentified disks and mergers depend on the definition of kinematic asymmetries and the classification threshold when using kinemetry-based classifications. Our results suggest that additional indicators such as morphologies traced by stars or molecular gas are required to further constrain the merger/disk classifications at high-z.

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