Dual-band Unified Exploration of Three CMZ Clouds (DUET). Cloud-wide census of continuum sources showing low spectral indices

Abstract

The Milky Way's Central Molecular Zone (CMZ) is measured to form stars 10 times less efficiently than in the Galactic disk, based on emission from high-mass stars. However, the CMZ's low-mass protostellar population, which accounts for most of the initial stellar mass budget and star formation rate (SFR), is poorly constrained observationally due to limited sensitivity and resolution. We present the Dual-band Unified Exploration of Three CMZ Clouds (DUET) survey, targeting the 20 km/s Cloud, Sgr C, and Dust Ridge cloud e using the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 and 3 mm. The mosaicked observations achieve a comparable resolution of 0.2-0.3" (~1600-2500 au) and a sky coverage of 8.3-10.4 square arcmin, respectively. We report 563 continuum sources at 1.3 mm and 330 at 3 mm, respectively, and a dual-band catalog with 450 continuum sources. These sources are marginally resolved at the 2,000 au resolution. We find a cloud-wide deviation (>70%) from commonly-used dust modified blackbody (MBB) models, characterized by either low spectral indices or low brightness temperatures. Three possible explanations for the deviation are discussed. (1) Optically thick Class 0/I Young stellar objects (YSOs) with very small beam filling factors can lead to lower brightness temperatures than what MBB models predict. (2) Large (mm/cm-sized) dust grains have more significant self-scattering, and therefore frequency-dependent albedo could cause lower spectral indices. (3) Free-free emission over 30 uJy can severely contaminate dust emission and cause low spectral indices for mJy sources in our sample, although the needed number of massive protostars (embedded UCHII regions) is infeasibly high for the normal stellar initial mass function. A reliable measurement of the SFR at low protostellar masses will require future work to distinguish between these possible explanations.

16 pages, 10 figures. Accepted for publication in A&A. For interactive data visualization, see https://xfengwei.github.io/magnifier/index.html. The continuum images will be available once the paper is published

References in corpus (30)

• CASA, the Common Astronomy Software Applications for Radio Astronomy
• The mass distribution in the Galactic Centre from interferometric astrometry of multiple stellar orbits
• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• Fragmentation of Molecular Clumps and Formation of Protocluster
• The anomalously low (sub)millimeter spectral indices of some protoplanetary disks may be explained by dust self-scattering
• The 1.28 GHz MeerKAT Galactic Center Mosaic
• A cluster in the making: ALMA reveals the initial conditions for high-mass cluster formation
• The Interplay between Star Formation and the Nuclear Environment of our Galaxy: Deep X-ray Observations of the Galactic Center Arches and Quintuplet Clusters
• ALMA-IMF I -- Investigating the origin of stellar masses: Introduction to the Large Program and first results
• The Central 1000 au of a Pre-stellar Core Revealed with ALMA. II. Almost Complete Freeze-out
• Multiscale, multiwavelength extraction of sources and filaments using separation of the structural components: getsf
• ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- XV. Steady Accretion from Global Collapse to Core Feeding in Massive Hub-filament System SDC335
• The ALMA Interferometric Pipeline Heuristics
• Tracing the Conversion of Gas into Stars in Young Massive Cluster Progenitors
• A multi-wavelength view of the Galactic center dust ridge reveals little star formation
• The Gould Belt Very Large Array Survey IV: The Taurus-Auriga complex
• CMZoom: Survey Overview and First Data Release
• "Ash-fall" induced by molecular outflow in protostar evolution
• Star Formation Rates of Massive Molecular Clouds in the Central Molecular Zone
• Radiation Transfer of Models of Massive Star Formation. IV. The Model Grid and Spectral Energy Distribution Fitting
• ALMA Observations of Massive Clouds in the Central Molecular Zone: Jeans Fragmentation and Cluster Formation
• Evidence for Large Grains in the Star-forming Filament OMC-2/3
• Massive and low-mass protostars in massive "starless" cores
• ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP) II. Survey overview: a first look at 1.3 mm continuum maps and molecular outflows
• Star formation in 'the Brick': ALMA reveals an active proto-cluster in the Galactic centre cloud G0.253+0.016
• ALMA Observations of Massive Clouds in the Central Molecular Zone: Ubiquitous Protostellar Outflows
• The SQUALO project (Star formation in QUiescent And Luminous Objects) I: clump-fed accretion mechanism in high-mass star-forming objects
• Dust grains cannot grow to millimeter sizes in protostellar envelopes
• A global view on star formation: The GLOSTAR Galactic plane survey. IX. Radio Source Catalog III: 2<l<28, 36<l<40, 56<l<60 and |b|<1, VLA B-configuration
• On the Scarcity of Dense Cores ($n>10^5$ cm${}^{-3}$) in High Latitude Planck Galactic Cold Clumps

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