Towards Studying Hierarchical Assembly in Real Time: A Milky Way Progenitor Galaxy at z = 2.36 under the Microscope

Abstract

We use Hubble Space Telescope (HST) imaging and near-infrared spectroscopy from Keck/MOSFIRE to study the sub-structure around the progenitor of a Milky Way-mass galaxy in the Hubble Frontier Fields (HFF). Specifically, we study an $r_e=40_{-30}^{+70}$pc, $M_{\star }\sim 10^{8.2}{M}_{\odot }$ rest-frame ultra-violet luminous "clump" at a projected distance of $\sim$100~pc from a $M_{\star }\sim 10^{9.8}$M${}_{\odot }$ galaxy at $z=2.36$ with a magnification $\mu =5.21$. We measure the star formation history of the clump and galaxy by jointly modeling the broadband spectral energy distribution from HST photometry and H$\alpha$ from MOSFIRE spectroscopy. Given our inferred properties (e.g., mass, metallicity, dust) of the clump and galaxy, we explore scenarios in which the clump formed \emph{in-situ} (e.g., a star forming complex) or \emph{ex-situ} (e.g., a dwarf galaxy being accreted). If it formed \emph{in-situ}, we conclude that the clump is likely a single entity as opposed to a aggregation of smaller star clusters, making it one of the most dense star clusters cataloged. If it formed \emph{ex-situ}, then we are witnessing an accretion event with a 1:40 stellar mass ratio. However, our data alone are not informative enough to distinguish between \emph{in-situ} and \emph{ex-situ} scenarios to a high level of significance. We posit that the addition of high-fidelity metallicity information, such as [OIII]4363Å, which can be detected at modest S/N with only a few hours of JWST/NIRSpec time, may be a powerful discriminant. We suggest that studying larger samples of moderately lensed sub-structures across cosmic time can provide unique insight into the hierarchical formation of galaxies like the Milky Way.

arXiv commentAccepted to MNRAS

References in corpus (75)

• dynesty: A Dynamic Nested Sampling Package for Estimating Bayesian Posteriors and Evidences
• Cold streams in early massive hot haloes as the main mode of galaxy formation
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• The ages and metallicities of galaxies in the local universe
• The New Galaxy: Signatures of its Formation
• Co-formation of the Galactic disc and the stellar halo
• An ultra-deep near-infrared spectrum of a compact quiescent galaxy at z=2.2
• A New Non-Parametric Approach to Galaxy Morphological Classification
• The SINS survey of z~2 galaxy kinematics: properties of the giant star forming clumps
• Star Clusters Across Cosmic Time
• The Frontier Fields: Survey Design
• The remnants of galaxy formation from a panoramic survey of the region around M31
• How to Measure Galaxy Star Formation Histories II: Nonparametric Models
• Deriving Physical Properties from Broadband Photometry with Prospector: Description of the Model and a Demonstration of its Accuracy Using 129 Galaxies in the Local Universe
• The Evolution of Galaxy Mergers and Morphology at z<1.2 in the Extended Groth Strip
• The spatial structure of mono-abundance sub-populations of the Milky Way disk
• The MOSFIRE Deep Evolution Field (MOSDEF) Survey: Rest-Frame Optical Spectroscopy for ~1500 H-Selected Galaxies at 1.37 < z < 3.8
• The Major and Minor Galaxy Merger Rates at z < 1.5
• The Dust Attenuation Law in Distant Galaxies: Evidence for Variation with Spectral Type
• Smooth(er) Stellar Mass Maps in CANDELS: Constraints on the Longevity of Clumps in High-redshift Star-forming Galaxies
• The Mass Distribution of SDSS J1004+4112 Revisited
• Toy Models for Galaxy Formation versus Simulations
• Constraints on the assembly and dynamics of galaxies. II. Properties of kiloparsec-scale clumps in rest-frame optical emission of z ~ 2 star-forming galaxies
• The Assembly of Milky Way-like Galaxies Since z~2.5
• Mass and magnification maps for the Hubble Space Telescope Frontier Fields clusters: implications for high redshift studies
• Multi-scale cluster lens mass mapping I. Strong Lensing modelling
• Lens models and magnification maps of the six Hubble Frontier Fields clusters
• Precise Strong Lensing Mass Modeling of Four Hubble Frontier Fields Clusters and a Sample of Magnified High-Redshift Galaxies
• Multi-Wavelength View of Kiloparsec-Scale Clumps in Star-Forming Galaxies at z~2
• Hubble Frontier Fields First Complete Cluster Data: Faint Galaxies at $z\sim 5-10$ for UV Luminosity Functions and Cosmic Reionization
• Size--luminosity relations and UV luminosity functions at $z=6-9$ simultaneously derived from the complete Hubble Frontier Fields data
• The Population of Giant Clumps in Simulated High-z Galaxies: In-situ and Ex-situ, Migration and Survival
• Stellar Feedback & Bulge Formation in Clumpy Disks
• Giant Clumps in Simulated High-z Galaxies: Properties, Evolution and Dependence on Feedback
• Hubble Frontier Fields : A High-Precision Strong-Lensing Mass Model of the Massive Galaxy Cluster Abell 2744 using 180 Multiple Images
• Studying the YMC population of M83: how long clusters remain embedded, their interaction with the ISM and implications for GC formation theories
• Morphologies of ~190,000 Galaxies at z=0-10 Revealed with HST Legacy Data II. Evolution of Clumpy Galaxies
• The Dragonfly Nearby Galaxies Survey. I. Substantial variation in the diffuse stellar halos around spiral galaxies
• The Andromeda galaxy's most important merger about 2 billion years ago as M32's likely progenitor
• Resolving the Discrepancy of Galaxy Merger Fraction Measurements at z ~ 0 - 3
• The Primeval Populations of the Ultra-Faint Dwarf Galaxies
• Giant clumps in the FIRE simulations: a case study of a massive high-redshift galaxy
• Focusing Cosmic Telescopes: Exploring Redshift z~5-6 Galaxies with the Bullet Cluster 1E0657-56
• The nature of giant clumps in distant galaxies probed by the anatomy of the Cosmic Snake
• Massive Star cluster formation under the microscope at z=6
• Clumpy Galaxies in CANDELS. II. Physical Properties of UV-bright Clumps at $0.5\le z<3$
• The GHOSTS survey. II. The diversity of Halo Color and Metallicity Profiles of Massive Disk Galaxies
• Comparing the Ancient Star Formation Histories of the Magellanic Clouds
• The sizes of $z\sim 6-8$ lensed galaxies from the Hubble Frontier Fields Abell 2744 data
• Forming Super Star Clusters in the Central Starburst of NGC 253
• The dust and [CII] morphologies of redshift ~4.5 sub-millimeter galaxies at ~200pc resolution: The absence of large clumps in the interstellar medium of high-redshift galaxies
• A lower fragmentation mass scale in high redshift galaxies and its implications on giant clumps: a systematic numerical study
• HFF-DeepSpace Photometric Catalogs of the Twelve Hubble Frontier Fields, Clusters and Parallels: Photometry, Photometric Redshifts, and Stellar Masses
• ALMA maps the Star-Forming Regions in a Dense Gas Disk at z~3
• Hubble Frontier Fields: The Geometry and Dynamics of the Massive Galaxy Cluster Merger MACSJ0416.1-2403
• Hubble Tarantula Treasury Project: Unraveling Tarantula's Web. II. Optical and Near Infrared Star Formation History of the Starburst Cluster NGC 2070 in 30 Doradus
• Tracing Galaxies Through Cosmic Time with Number Density Selection
• The Physical Conditions in a Pre Super Star Cluster Molecular Cloud in the Antennae Galaxies
• ALMA 200-parsec Resolution Imaging of Smooth Cold Dusty Disks in Typical $z\sim 3$ Star-Forming Galaxies
• A contribution of star-forming clumps and accreting satellites to the mass assembly of z ~ 2 galaxies
• Extremely Small Sizes for Faint z~2-8 Galaxies in the Hubble Frontier Fields: A Key Input For Establishing their Volume Density and UV Emissivity
• Phylogeny of the Milky Way's inner disk and bulge populations: Implications for gas accretion, (the lack of) inside-out thick disk formation, and quenching
• Halos of Spiral Galaxies. I. The Tip of the Red Giant Branch as a Distance Indicator
• On the stellar masses of giant clumps in distant star-forming galaxies
• An extremely young massive clump forming by gravitational collapse in a primordial galaxy
• Fossil remnants of reionization in the halo of the Milky Way
• Accurate Identification of Galaxy Mergers with Imaging
• Formation of Metal-Poor Globular Clusters in Lyman alpha Emitting Galaxies in the Early Universe
• Galaxy Formation as a Cosmological Tool. I: The Galaxy Merger History as a Measure of Cosmological Parameters
• Clumpy galaxies seen in H-alpha: inflated observed clump properties due to limited spatial resolution and sensitivity
• The VIMOS Ultra-Deep Survey: A major merger origin for the high fraction of galaxies at $2<z<6$ with two bright clump
• Very low-luminosity galaxies in the early universe have observed sizes similar to single star cluster complexes
• Searching for GC-like abundance patterns in young massive clusters
• The Detection of [O III]$\lambda$4363 in a Lensed, Dwarf Galaxy at $z$ = 2.59: Testing Metallicity Indicators and Scaling Relations at High Redshift and Low Mass
• Identifying mergers using non-parametric morphological classification at high redshifts

Cited by in corpus (9)

• The MUSE Deep Lensed Field on the Hubble Frontier Field MACS~J0416
• Stellar Masses of Giant Clumps in CANDELS and Simulated Galaxies Using Machine Learning
• RELICS: Small-scale Star Formation in Lensed Galaxies at $z=6-10$
• Fraction of Clumpy Star-Forming Galaxies at $0.5\le z\le 3$ in UVCANDELS: Dependence on Stellar Mass and Environment
• Clumps as multiscale structures in cosmic noon galaxies
• Investigating Clumpy Galaxies in the Sloan Digital Sky Survey Stripe 82 using the Galaxy Zoo
• The contribution of globular clusters to cosmic reionization
• On the Reionization-Era Globular Cluster in Low-Mass Galaxy Eridanus II
• Low-luminosity galaxies in the early universe have observed sizes similar to star cluster complexes