arXiv subjects

Jeffrey Newman

Publications and source records attributed to Jeffrey Newman.

18 recordsLinked to original sources

arXiv2022

Multiplicity Statistics of Stars in the Sagittarius Dwarf Spheroidal Galaxy: Comparison to the Milky Way

We use time-resolved spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) to examine the distribution of radial velocity (RV) variations in 249 stars identified as members of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy by Hayes et al (2020). We select Milky Way (MW) stars that have stellar parameters ($log(g)$, $T_{eff}$, and $[Fe/H]$) similar to those of the Sagittarius members by means of a k-d tree of dimension 3. We find that the shape of the distribution of RV shifts in Sgr dSph stars is similar to that measured in their MW analogs, but the total fraction of RV variable stars in the Sgr dSph is larger by a factor of $\sim 2$. After ruling out other explanations for this difference, we conclude that the fraction of close binaries in the Sgr dSph is intrinsically higher than in the MW. We discuss the implications of this result for the physical processes leading to the formation of close binaries in dwarf spheroidal and spiral galaxies.

astro-ph.GA↗

arXiv2021

The RR Lyrae Delay-Time Distribution: A Novel Perspective on Models of Old Stellar Populations

The delay-time distribution (DTD) is the occurrence rate of a class of objects as a function of time after a hypothetical burst of star formation. DTDs are mainly used as a statistical test of stellar evolution scenarios for supernova progenitors, but they can be applied to many other classes of astronomical objects. We calculate the first DTD for RR Lyrae variables using 29,810 RR Lyrae from the OGLE-IV survey and a map of the stellar-age distribution (SAD) in the Large Magellanic Cloud (LMC). We find that $\sim 46\%$ of the OGLE-IV RR Lyrae are associated with delay-times older than 8 Gyr (main-sequence progenitor masses less than 1 M$_{\odot}$), and consistent with existing constraints on their ages, but surprisingly about $51\%$ of RR Lyrae appear have delay times $1.2-8$ Gyr (main-sequence masses between $1 - 2$ M$_{\odot}$ at LMC metallicity). This intermediate-age signal also persists outside the Bar-region where crowding is less of a concern, and we verified that without this signal, the spatial distribution of the OGLE-IV RR Lyrae is inconsistent with the SAD map of the LMC. Since an intermediate-age RR Lyrae channel is in tension with the lack of RR Lyrae in intermediate-age clusters (noting issues with small-number statistics), and the age-metallicity constraints of LMC stars, our DTD result possibly indicates that systematic uncertainties may still exist in SAD measurements of old-stellar populations, perhaps stemming from the construction methodology or the stellar evolution models used. We described tests to further investigate this issue.

astro-ph.SR↗

arXiv2020

Are the Milky Way and Andromeda unusual? A comparison with Milky Way and Andromeda Analogs

Our Milky Way provides a unique test case for galaxy evolution models, thanks to our privileged position within the Milky Way's disc. This position also complicates comparisons between the Milky Way and external galaxies, due to our inability to observe the Milky Way from an external point of view. Milky Way analog galaxies offer us a chance to bridge this divide by providing the external perspective that we otherwise lack. However, over-precise definitions of "analog" yield little-to-no galaxies, so it is vital to understand which selection criteria produce the most meaningful analog samples. To address this, we compare the properties of complementary samples of Milky Way analogs selected using different criteria. We find the Milky Way to be within 1$σ$ of its analogs in terms of star-formation rate and bulge-to-total ratio in most cases, but we find larger offsets between the Milky Way and its analogs in terms of disc scale length; this suggests that scale length must be included in analog selections in addition to other criteria if the most accurate analogs are to be selected. We also apply our methodology to the neighbouring Andromeda galaxy. We find analogs selected on the basis of strong morphological features to display much higher star-formation rates than Andromeda, and we also find analogs selected on Andromeda's star-formation rate to over-predict Andromeda's bulge extent. This suggests both structure and star-formation rate should be considered when selecting the most stringent Andromeda analogs.

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arXiv2019

The Maunakea Spectroscopic Explorer

The Maunakea Spectroscopic Explorer is a next-generation massively multiplexed spectroscopic facility currently under development in Hawaii. It is completely dedicated to large-scale spectroscopic surveys and will enable transformative science. In this white paper we summarize the science case and describe the current state of the project.

astro-ph.IM↗

arXiv2019

Can intrinsic alignments of elongated low-mass galaxies be used to map the cosmic web at high redshift?

Hubble Space Telescope observations show that low-mass ($M_*=10^9-10^{10}M_{\odot}$) galaxies at high redshift ($z=1.0-2.5$) tend to be elongated (prolate) rather than disky (oblate) or spheroidal. This is explained in zoom-in cosmological hydrodynamical simulations by the fact that these galaxies are forming in cosmic web filaments where accretion happens preferentially along the direction of elongation. We ask whether the elongated morphology of these galaxies allows them to be used as effective tracers of cosmic web filaments at high redshift via their intrinsic alignments. Using mock lightcones and spectroscopically-confirmed galaxy pairs from the CANDELS survey, we test two types of alignments: (1) between the galaxy major axis and the direction to nearby galaxies of any mass, and (2) between the major axes of nearby pairs of low-mass, likely prolate, galaxies. The mock lightcones predict strong signals in 3D real space, 3D redshift space, and 2D projected redshift space for both types of alignments (assuming prolate galaxy orientations are the same as those of their host prolate halos), but we do not detect significant alignment signals in CANDELS observations. However, we show that spectroscopic redshifts have been obtained for only a small fraction of highly elongated galaxies, and accounting for spectroscopic incompleteness and redshift errors significantly degrades the 2D mock signal. This may partly explain the alignment discrepancy and highlights one of several avenues for future work.

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arXiv2017

Science-Driven Optimization of the LSST Observing Strategy

The Large Synoptic Survey Telescope is designed to provide an unprecedented optical imaging dataset that will support investigations of our Solar System, Galaxy and Universe, across half the sky and over ten years of repeated observation. However, exactly how the LSST observations will be taken (the observing strategy or "cadence") is not yet finalized. In this dynamically-evolving community white paper, we explore how the detailed performance of the anticipated science investigations is expected to depend on small changes to the LSST observing strategy. Using realistic simulations of the LSST schedule and observation properties, we design and compute diagnostic metrics and Figures of Merit that provide quantitative evaluations of different observing strategies, analyzing their impact on a wide range of proposed science projects. This is work in progress: we are using this white paper to communicate to each other the relative merits of the observing strategy choices that could be made, in an effort to maximize the scientific value of the survey. The investigation of some science cases leads to suggestions for new strategies that could be simulated and potentially adopted. Notably, we find motivation for exploring departures from a spatially uniform annual tiling of the sky: focusing instead on different parts of the survey area in different years in a "rolling cadence" is likely to have significant benefits for a number of time domain and moving object astronomy projects. The communal assembly of a suite of quantified and homogeneously coded metrics is the vital first step towards an automated, systematic, science-based assessment of any given cadence simulation, that will enable the scheduling of the LSST to be as well-informed as possible.

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arXiv2017

The Nature of Massive Transition Galaxies in CANDELS, GAMA, and Cosmological Simulations

We explore observational and theoretical constraints on how galaxies might transition between the "star-forming main sequence" (SFMS) and varying "degrees of quiescence" out to $z=3$. Our analysis is focused on galaxies with stellar mass $M_*>10^{10}M_{\odot}$, and is enabled by GAMA and CANDELS observations, a semi-analytic model (SAM) of galaxy formation, and a cosmological hydrodynamical "zoom in" simulation with momentum-driven AGN feedback. In both the observations and the SAM, transition galaxies tend to have intermediate Sérsic indices, half-light radii, and surface stellar mass densities compared to star-forming and quiescent galaxies out to $z=3$. We place an observational upper limit on the average population transition timescale as a function of redshift, finding that the average high-redshift galaxy is on a "fast track" for quenching whereas the average low-redshift galaxy is on a "slow track" for quenching. We qualitatively identify four physical origin scenarios for transition galaxies in the SAM: oscillations on the SFMS, slow quenching, fast quenching, and rejuvenation. Quenching timescales in both the SAM and the hydrodynamical simulation are not fast enough to reproduce the quiescent population that we observe at $z\sim3$. In the SAM, we do not find a clear-cut morphological dependence of quenching timescales, but we do predict that the mean stellar ages, cold gas fractions, SMBH masses, and halo masses of transition galaxies tend to be intermediate relative to those of star-forming and quiescent galaxies at $z<3$.

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arXiv2016

The evolution of the [OII], Hβ and [OIII] emission-line luminosity functions over the last nine billions years

Emission line galaxies are one of the main tracers of the large-scale structure to be targeted by the next-generation dark energy surveys. To provide a better understanding of the properties and statistics of these galaxies, we have collected spectroscopic data from the VVDS and DEEP2 deep surveys and estimated the galaxy luminosity functions (LFs) of three distinct emission lines, [OII] ($0.5 < z < 1.3$), Hβ ($0.3 < z < 0.8$) and [OIII] ($0.3 < z < 0.8$). Our measurements are based on 35,639 emission line galaxies and cover a volume of $\sim10^7$Mpc$^3$. We present the first measurement of the Hβ LF at these redshifts. We have also compiled LFs from the literature that were based on independent data or covered different redshift ranges, and we fit the entire set over the whole redshift range with analytic Schechter and Saunders models, assuming a natural redshift dependence of the parameters. We find that the characteristic luminosity ($L_*$) and density ($ϕ_*$) of all LFs increase with redshift. Using the Schechter model over the redshift ranges considered, we find that, for [OII] emitters, the characteristic luminosity $L_*(z=0.5)=3.2\times10^{41}$ erg/s increases by a factor of $2.7 \pm 0.2$ from z=0.5 to 1.3; for Hβ emitters $L_*(z=0.3)=1.3\times10^{41}$ erg/s increases by a factor of $2.0 \pm 0.2$ from z=0.3 to 0.8; and for [OIII] emitters $L_*(z=0.3)=7.3\times10^{41}$ erg/s increases by a factor of $3.5 \pm 0.4$ from z=0.3 to 0.8.

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arXiv2015

Near-ultraviolet Spectroscopy of Star-forming Galaxies from eBOSS: Signatures of Ubiquitous Galactic-scale Outflows

We present the rest-frame near-ultraviolet (NUV) spectroscopy of star-forming galaxies (SFGs) at 0.6 0.6. We use the data from the pilot observations of this program, including 8620 spectra of SFGs at 0.6<z<1.2. The median composite spectra of these SFGs at 2200 Ang < λ< 4000 Ang feature asymmetric, preferentially blueshifted non-resonant emission, Fe II*, and blueshifted resonant absorption, e.g., Fe II and Mg II, indicating ubiquitous outflows driven by star formation at these redshifts. For the absorption lines, we find a variety of velocity profiles with different degrees of blueshift. Comparing our new observations with the literature, we do not observe the non-resonant emission in the small-aperture (<40 pc) spectra of local star-forming regions with the Hubble Space Telescope, and find the observed line ratios in the SFG spectra to be different from those in the spectra of local star-forming regions, as well as those of quasar absorption-line systems in the same redshift range. We introduce an outflow model that can simultaneously explain the multiple observed properties and suggest that the variety of absorption velocity profiles and the line ratio differences are caused by scattered fluorescent emission filling in on top of the absorption in the large-aperture eBOSS spectra. We develop an observation-driven, model-independent method to correct the emission-infill to reveal the true absorption profiles. Our results show that eBOSS and future dark-energy surveys (e.g., DESI and PFS) will provide rich datasets of NUV spectroscopy for astrophysical applications.

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arXiv2014

Evidence for (and Against) Progenitor Bias in the Size Growth of Compact Red Galaxies

Most massive passive galaxies are compact at high redshifts, but similarly compact massive galaxies are rare in the local universe. The most common interpretation of this phenomenon is that massive galaxies have grown in size by a factor of about five since redshift z=2. An alternative explanation is that recently quenched massive galaxies are larger (a "progenitor bias"). In this paper we explore the importance of progenitor bias by looking for systematic differences in the stellar populations of compact early-type galaxies in the DEEP2 survey as a function of size. Our analysis is based on applying the statistical technique of bootstrap resampling to constrain differences in the median ages of our samples and to begin to characterize the distribution of stellar populations in our co-added spectra. The light-weighted ages of compact early-type galaxies at redshifts 0.5 < z < 1.4 are compared to those of a control sample of larger galaxies at similar redshifts. We find that massive compact early-type galaxies selected on the basis of red color and high bulge-to-total ratio are younger than similarly selected larger galaxies, suggesting that size growth in these objects is not driven mainly by progenitor bias, and that individual galaxies grow as their stellar populations age. However, compact early-type galaxies selected on the basis of image smoothness and high bulge-to-total ratio are older than a control sample of larger galaxies. Progenitor bias will play a significant role in defining the apparent size changes of early-type galaxies if they are selected on the basis of the smoothness of their light distributions.

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arXiv2014

Estimating the distribution of Galaxy Morphologies on a continuous space

The incredible variety of galaxy shapes cannot be summarized by human defined discrete classes of shapes without causing a possibly large loss of information. Dictionary learning and sparse coding allow us to reduce the high dimensional space of shapes into a manageable low dimensional continuous vector space. Statistical inference can be done in the reduced space via probability distribution estimation and manifold estimation.

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arXiv2013

Widespread and Hidden Active Galactic Nuclei in Star-Forming Galaxies at Redshift > 0.3

We characterize the incidence of active galactic nuclei (AGNs) is 0.3 < z < 1 star-forming galaxies by applying multi-wavelength AGN diagnostics (X-ray, optical, mid-infrared, radio) to a sample of galaxies selected at 70-micron from the Far-Infrared Deep Extragalactic Legacy survey (FIDEL). Given the depth of FIDEL, we detect "normal" galaxies on the specific star formation rate (sSFR) sequence as well as starbursting systems with elevated sSFR. We find an overall high occurrence of AGN of 37+/-3%, more than twice as high as in previous studies of galaxies with comparable infrared luminosities and redshifts but in good agreement with the AGN fraction of nearby (0.05 < z < 0.1) galaxies of similar infrared luminosities. The more complete census of AGNs comes from using the recently developed Mass-Excitation (MEx) diagnostic diagram. This optical diagnostic is also sensitive to X-ray weak AGNs and X-ray absorbed AGNs, and reveals that absorbed active nuclei reside almost exclusively in infrared-luminous hosts. The fraction of galaxies hosting an AGN appears to be independent of sSFR and remains elevated both on the sSFR sequence and above. In contrast, the fraction of AGNs that are X-ray absorbed increases substantially with increasing sSFR, possibly due to an increased gas fraction and/or gas density in the host galaxies.

astro-ph.CO↗

arXiv2012

Addressing Decadal Survey Science through Community Access to Highly Multiplexed Spectroscopy with BigBOSS on the KPNO Mayall Telescope

This document summarizes the results of a community-based discussion of the potential science impact of the Mayall+BigBOSS highly multiplexed multi-object spectroscopic capability. The KPNO Mayall 4m telescope equipped with the DOE- and internationally-funded BigBOSS spectrograph offers one of the most cost-efficient ways of accomplishing many of the pressing scientific goals identified for this decade by the "New Worlds, New Horizons" report. The BigBOSS Key Project will place unprecedented constraints on cosmological parameters related to the expansion history of the universe. With the addition of an open (publicly funded) community access component, the scientific impact of BigBOSS can be extended to many important astrophysical questions related to the origin and evolution of galaxies, stars, and the IGM. Massive spectroscopy is the critical missing ingredient in numerous ongoing and planned ground- and space-based surveys, and BigBOSS is unique in its ability to provide this to the US community. BigBOSS data from community-led projects will play a vital role in the education and training of students and in maintaining US leadership in these fields of astrophysics. We urge the NSF-AST division to support community science with the BigBOSS multi-object spectrograph through the period of the BigBOSS survey in order to ensure public access to the extraordinary spectroscopic capability.

astro-ph.CO↗

arXiv2012

Dependence of Galaxy Quenching on Halo Mass and Distance from its Centre

We study the dependence of star-formation quenching on galaxy mass and environment, in the SDSS (z~0.1) and the AEGIS (z~1). It is crucial that we define quenching by low star-formation rate rather than by red colour, given that one third of the red galaxies are star forming. We address stellar mass M*, halo mass Mh, density over the nearest N neighbours deltaN, and distance to the halo centre D. The fraction of quenched galaxies appears more strongly correlated with Mh at fixed M* than with M* at fixed Mh, while for satellites quenching also depends on D. We present the M*-Mh relation for centrals at z~1. At z~1, the dependence of quenching on M* at fixed Mh is somewhat more pronounced than at z~0, but the quenched fraction is low (10%) and the haloes are less massive. For satellites, M*-dependent quenching is noticeable at high D, suggesting a quenching dependence on sub-halo mass for recently captured satellites. At small D, where satellites likely fell in more than a few Gyr ago, quenching strongly depends on Mh, and not on M*. The Mh-dependence of quenching is consistent with theoretical wisdom where virial shock heating in massive haloes shuts down accretion and triggers ram-pressure stripping, causing quenching. The interpretation of deltaN is complicated by the fact that it depends on the number of observed group members compared to N, motivating the use of D as a better measure of local environment.

astro-ph.CO↗

arXiv2012

On The Detection Of Ionizing Radiation Arising From Star-Forming Galaxies At Redshift z ~ 3-4 : Looking For Analogs Of "Stellar Reionizers"

We use the spatially-resolved, multi-band photometry in the GOODS South field acquired by the CANDELS project to constrain the nature of candidate Lyman continuum (LyC) emitters at redshift z~3.7 identified using ultra-deep imaging below the Lyman limit (1-sigma limit of ~30 AB in a 2" diameter aperture). In 18 candidates, out of a sample of 19 with flux detected at >3-sigma level, the light centroid of the candidate LyC emission is offset from that of the LBG by up to 1.5". We fit the SED of the LyC candidates to spectral population synthesis models to measure photometric redshifts and the stellar population parameters. We also discuss the differences in the UV colors between the LBG and the LyC candidates, and how to estimate the escape fraction of ionizing radiation (f_esc) in cases, like in most of our galaxies, where the LyC emission is spatially offset from the host galaxy. In all but one case we conclude that the candidate LyC emission is most likely due to lower redshift interlopers. Based on these findings, we argue that the majority of similar measurements reported in the literature need further investigation before it can be firmly concluded that LyC emission is detected. Our only surviving LyC candidate is a LBG at z=3.795, which shows the bluest (B-V) color among LBGs at similar redshift, a stellar mass of M~2 x 10^9 Msun, weak interstellar absorption lines and a flat UV spectral slope with no Lya in emission. We estimate its f_esc to be in the range 25%-100%, depending on the dust and intergalactic attenuation.

astro-ph.CO↗

arXiv2002

Deviations from the Local Hubble Flow. I. The Tip of the Red Giant Branch as a Distance Indicator

The properties of the velocity field in the local volume (cz < 550 km/s) have been difficult to constrain due to a lack of a consistent set of galaxy distances. The sparse observations available to date suggest a remarkably quiet flow, with little deviation from a pure Hubble law. However, velocity field models based on the distribution of galaxies in the 1.2 Jy IRAS redshift survey, predict a quadrupolar flow pattern locally with strong infall at the poles of the local Supergalactic plane. We probe this velocity field and begin to establish a consistent set of galactic distances. We have obtained images of nearby galaxies in the I and V band from the W.M. Keck Observatory and in F814W and F555W filters from the Hubble Space Telescope. Where these galaxies are well resolved into stars we may use the Tip of the Red Giant Branch (TRGB) as a distance indicator. Using a maximum likelihood analysis to quantitatively measure the I magnitude of the TRGB we determine precise distances to seven nearby galaxies: Leo I, Sextans B, NGC 1313, NGC 3109, UGC 03755, UGC 06456, and UGC 07577.

astro-ph↗

arXiv2001

Mining the Sky with Redshift Surveys

Since the late 1970's, redshift surveys have been vital for progress in understanding large-scale structure in the Universe. The original CfA redshift survey collected spectra of 20-30 galaxies per clear night on a 1.5 meter telescope; over a two year period the project added ~2000 new redshifts to the literature. Subsequent low-z redshift surveys have been up to an order of magnitude larger, and ongoing surveys will yield a similar improvement over the generation preceding them. Full sky redshift surveys have a special role to play as predictors of cosmological flows, and deep pencil beam surveys have provided fundamental constraints on the evolution of properties of galaxies. With the 2DF redshift survey and the SDSS survey, our knowledge of the statistical clustering of low-redshift galaxies will achieve unprecedented precision. Measurements of clustering in the distant Universe are more limited at present, but will become much better in this decade as the VLT/VIRMOS and Keck/DEIMOS projects produce results. As in so many other fields, progress in large scale structure studies, both observational and theoretical, has been made possible by improvements in technologies, especially computing. This review briefly highlights twenty years of progress in this evolving discipline and describes a few novel cosmological tests that will be attempted with the Keck/DEIMOS survey.

astro-ph↗

arXiv2000

The DEEP2 Redshift Survey

The DEIMOS spectrograph is nearing completion in the UC Lick shops and will be delivered to the Keck Observatory in 2001. Once it is operational, a team of astronomers will initiate DEEP2, a major redshift survey of galaxies that will consume approximately 120 nights at the Keck Observatory over a three year period. Our goal is to gather high-quality spectra of ~60,000 galaxies with Z>0.7 in order to study the properties and large scale clustering of galaxies at $Z \approx 1$. The survey will be done at high spectral resolution, R=λ/Δλ~3500, allowing us to work between the bright OH sky emission lines and to infer linewidths for many of the target galaxies. The linewidth data will facilitate the execution of the classical redshift-volume cosmological test, which can provide a precision measurement of the equation of state of the Universe.

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