arXiv subjects

Natalie Butterfield

Publications and source records attributed to Natalie Butterfield.

15 recordsLinked to original sources

arXiv2026

ACES VIII: A Survey of Compact, High-Velocity Features Observed in CS(2-1)

The extreme kinematics of the Milky Way's Central Molecular Zone (CMZ) are influenced by processes such as dynamical shearing, cloud collisions, and stellar feedback. These events are visible in molecular data as vertically spiked features in position-velocity (PV) diagrams referred to as high velocity dispersion compact clouds (HVCCs). Using ALMA CMZ Exploration Survey (ACES) CS (2-1) molecular data, we identify a total of 235 HVCC candidates, 163 of which are visually identified, and an additional 72 identified via automated dendrogram methods. For each HVCC we catalog and report the physical and kinematic properties, explore line ratios of the cold dense gas tracer \HNCO with C-shock tracers, classify the morphology of their PV diagrams, and view their position-position-velocity distribution. The sample includes structures which are compact (d<5 pc) and have large velocity extents (20 km/s $<\Delta \mathrm{V} <$ 140 km/s), with most structures showing thin, `spiked' PV morphologies. We highlight areas of high ratios between HNCO and C-shock tracers along the edge of known orbital streams, implying a buildup of bar lane gas accreting onto the CMZ. We also find a collection of HVCCs overlapping with the 50 km/s cloud and known circumnuclear disk features. This catalog will be used for future investigation of nuclear inflow and determining dominant mechanisms disrupting average CMZ gas flows.

astro-ph.GA↗

arXiv2025

Parallel Alignments between Magnetic Fields and Dense Structures in the Central Molecular Zone

The recent Far-Infrared Polarimetric Large-Area Central Molecular Zone Exploration (FIREPLACE) survey with SOFIA has mapped plane-of-the-sky magnetic field orientations within the Central Molecular Zone (CMZ) of the Milky Way. Applying the Histogram of Relative Orientation (HRO) analysis to the FIREPLACE data, we find that the relative orientation between magnetic fields and column density structures is random in low-density regions (2x10^22 10^23 cm^{-2}). This trend is in contrast with that of the nearby molecular clouds, where the relative orientation transitions from parallel to perpendicular with increasing column densities. However, the relative orientation varies between individual CMZ clouds. Comparisons with MHD simulations specific to the CMZ conditions suggest that the observed parallel alignment is intrinsic rather than artifacts caused by the projection effect. The origin of this parallel configuration may arise from the fact that most dense structures in the CMZ are not self-gravitating, as they are in super-virial states, except for the mini-starburst region Sgr B2. These findings are consistent with the low star formation efficiency observed in the CMZ compared to that in the Galactic disk.

astro-ph.GA↗

arXiv2025

Discovery of a Giant Molecular Cloud at the Midpoint of the Galactic Bar Dust Lanes: M4.7-0.8

We present the detection of a previously unknown giant molecular cloud (GMC) located at the midpoint of the Galactic Bar Dust Lanes (M4.7--0.8), using spectral line observations taken with the Green Bank Telescope (GBT). This $\sim$60 pc long GMC is associated with accreting material that is transitioning from the quieter Galactic disk environment to the more extreme central molecular zone (CMZ) environment. Our 24 GHz single-dish radio observations targeted the NH$_3$ (1,1)$-$(4,4) and HC$_5$N (9$-$8), known dense gas tracers. The observations reveal the main features of the GMC, which we have dubbed the `Nexus' and `Filament', covering a 0$.\!\!^\circ$5$\times$0$.\!\!^\circ$25 area at 31$''$ angular resolution. In this publication we investigate the gas kinematics within the observed region and compare the distribution of molecular emission to previous infrared surveys to better understand the dust component. The observed gas tracers show centrally condensed cores corresponding to the positions of high dust column densities and low dust temperatures. We report the detection of a previously unknown NH$_3$ (3,3) maser, along with a 70$\mu$m source association, which supports the identification of this region as being actively star-forming. Gas emission in this region shows broad linewidths, comparable to values seen in CMZ clouds. The overall description of this cloud that we present is that of a highly dynamic region comprising dense gas and dust. This encapsulates a wide range of features associated with star formation, in addition to material transport related to the CMZ.

astro-ph.GA↗

arXiv2025

The Complex Magnetic Field of the Extreme Galactic Center: PRIMA Science Potential

The Central Molecular Zone (CMZ) of the Galactic Center (GC) region of the Milky Way contains a substantial fraction of the molecular mass of the Galaxy >10e7 solar masses yet exhibits an order of magnitude lower star formation efficiency (SFE) than expected given the high densities found in this region. There are multiple possible explanations for the depressed SFE in the CMZ, like feedback, strong turbulence, longer free-fall timescales, and high magnetic field strengths. It is currently unclear which of these mechanisms is the dominant inhibitor of star formation in the CMZ. It is important to understand the star formation process in the extreme environment of the CMZ because it is the only Galactic nuclear region we are able to study at high spatial resolutions with current observatories. One way to determine the relative importance of the different SFE inhibiting mechanisms is through multi-spatial and multi-frequency polarimetric observations of the CMZ. Such observations will provide insight into the behavior of the magnetic field in this unique environment. These observations will complement radio observations of non-thermal structures revealing the magnetic field morphology and polarization. The PRobe far--Infrared Mission for Astrophysics (PRIMA) will be uniquely capable of contributing to such explorations by providing unique resolutions and frequencies for polarimetric observations. The PRIMAger instrument will yield polarimetric observations covering the wavelength range 80 -- 261 um with beam sizes ranging from 11 -- 28'', capabilities that complement existing and upcoming observatories.

astro-ph.GA↗

arXiv2024

Polarized Light from Massive Protoclusters (POLIMAP). I. Dissecting the role of magnetic fields in the massive infrared dark cloud G28.37+0.07

Magnetic fields may play a crucial role in setting the initial conditions of massive star and star cluster formation. To investigate this, we report SOFIA-HAWC+ $214\:μ$m observations of polarized thermal dust emission and high-resolution GBT-Argus C$^{18}$O(1-0) observations toward the massive Infrared Dark Cloud (IRDC) G28.37+0.07. Considering the local dispersion of $B$-field orientations, we produce a map of $B$-field strength of the IRDC, which exhibits values between $\sim0.03 - 1\:$mG based on a refined Davis-Chandrasekhar-Fermi (r-DCF) method proposed by Skalidis \& Tassis. Comparing to a map of inferred density, the IRDC exhibits a $B-n$ relation with a power law index of $0.51\pm0.02$, which is consistent with a scenario of magnetically-regulated anisotropic collapse. Consideration of the mass-to-flux ratio map indicates that magnetic fields are dynamically important in most regions of the IRDC. A virial analysis of a sample of massive, dense cores in the IRDC, including evaluation of magnetic and kinetic internal and surface terms, indicates consistency with virial equilibrium, sub-Alfvénic conditions and a dominant role for $B-$fields in regulating collapse. A clear alignment of magnetic field morphology with direction of steepest column density gradient is also detected. However, there is no preferred orientation of protostellar outflow directions with the $B-$field. Overall, these results indicate that magnetic fields play a crucial role in regulating massive star and star cluster formation and so need to be accounted for in theoretical models of these processes.

astro-ph.GA↗

arXiv2023

CMZoom IV. Incipient High-Mass Star Formation Throughout the Central Molecular Zone

In this work, we constrain the star-forming properties of all possible sites of incipient high-mass star formation in the Milky Way's Galactic Center. We identify dense structures using the CMZoom 1.3mm dust continuum catalog of objects with typical radii of $\sim$0.1pc, and measure their association with tracers of high-mass star formation. We incorporate compact emission at 8, 21, 24, 25, and 70um from MSX, Spitzer, Herschel, and SOFIA, catalogued young stellar objects, and water and methanol masers to characterize each source. We find an incipient star formation rate (SFR) for the CMZ of ~0.08 Msun yr^{-1} over the next few 10^5 yr. We calculate upper and lower limits on the CMZ's incipient SFR of ~0.45 Msun yr^{-1} and ~0.05 Msun yr^{-1} respectively, spanning between roughly equal to and several times greater than other estimates of CMZ's recent SFR. Despite substantial uncertainties, our results suggest the incipient SFR in the CMZ may be higher than previously estimated. We find that the prevalence of star formation tracers does not correlate with source volume density, but instead ~75% of high-mass star formation is found in regions above a column density ratio (N_{SMA}/N_{Herschel}) of ~1.5. Finally, we highlight the detection of ``atoll sources'', a reoccurring morphology of cold dust encircling evolved infrared sources, possibly representing HII regions in the process of destroying their envelopes.

astro-ph.GA↗

arXiv2023

Widespread Hot Ammonia in the Central Kiloparsec of the Milky Way

The inner 300-500 pc of the Milky Way has some of the most extreme gas conditions in our Galaxy. Physical properties of the Central Molecular Zone (CMZ), including temperature, density, thermal pressure, and turbulent pressure, are key factors for characterizing gas energetics, kinematics, and evolution. The molecular gas in this region is more than an order of magnitude hotter than gas in the Galactic disk, but the mechanism responsible for heating the gas remains uncertain. We characterize the temperature for 16 regions, extending out to a projected radius of $\sim$450 pc. We observe \am\, J,K=(1,1)-(6,6) inversion transitions from SWAG (Survey of Water and Ammonia in the Galactic Center) using the Australia Telescope Compact Array (ATCA), and ammonia lines (J,K) = (8,8)-(14,14) using the 100\,m Green Bank Telescope. Using these two samples we create full Boltzmann plots for every source and fit two rotational temperature components to the data. For the cool component we detect rotational temperatures ranging from 20-80\,K, and for the hot component we detect temperature ranging from 210-580\,K. With this sample of 16 regions, we identify some of the most extreme molecular gas temperatures detected in the Galactic center thus far. We do not find a correlation between gas temperature and Galactocentric radius, and we confirm that these high temperatures are not exclusively associated with actively star-forming clouds. We also investigate temperature and line widths and find (1) no correlation between temperature and line width and (2) the lines are non-thermally broadened indicating that non-thermal motions are dominant over thermal.

astro-ph.GA↗

arXiv2023

CMZoom III: Spectral Line Data Release

We present an overview and data release of the spectral line component of the SMA Large Program, \textit{CMZoom}. \textit{CMZoom} observed $^{12}$CO(2-1), $^{13}$CO(2-1) and C$^{18}$O(2-1), three transitions of H$_{2}$CO, several transitions of CH$_{3}$OH, two transitions of OCS and single transitions of SiO and SO, within gas above a column density of N(H$_2$)$\ge 10^{23}$\,cm$^{-2}$ in the Central Molecular Zone (CMZ; inner few hundred pc of the Galaxy). We extract spectra from all compact 1.3\,mm \emph{CMZoom} continuum sources and fit line profiles to the spectra. We use the fit results from the H$_{2}$CO 3(0,3)-2(0,2) transition to determine the source kinematic properties. We find $\sim 90$\% of the total mass of \emph{CMZoom} sources have reliable kinematics. Only four compact continuum sources are formally self-gravitating. The remainder are consistent with being in hydrostatic equilibrium assuming that they are confined by the high external pressure in the CMZ. Based on the mass and density of virially bound sources, and assuming star formation occurs within one free-fall time with a star formation efficiency of $10\% - 75\%$, we place a lower limit on the future embedded star-formation rate of $0.008 - 0.06$\,M$_{\odot}$\,yr$^{-1}$. We find only two convincing proto-stellar outflows, ruling out a previously undetected population of very massive, actively accreting YSOs with strong outflows. Finally, despite having sufficient sensitivity and resolution to detect high-velocity compact clouds (HVCCs), which have been claimed as evidence for intermediate mass black holes interacting with molecular gas clouds, we find no such objects across the large survey area.

astro-ph.GA↗

arXiv2020

CMZoom II: Catalog of Compact Submillimeter Dust Continuum Sources in the Milky Way's Central Molecular Zone

In this paper we present the CMZoom Survey's catalog of compact sources (< 10'', ~0.4pc) within the Central Molecular Zone (CMZ). CMZoom is a Submillimeter Array (SMA) large program designed to provide a complete and unbiased map of all high column density gas (N(H$_2$) $\geq$ 10$^{23}$ cm$^{-2}$) of the innermost 500pc of the Galaxy in the 1.3mm dust continuum. We generate both a robust catalog designed to reduce spurious source detections, and a second catalog with higher completeness, both generated using a pruned dendrogram. In the robust catalog, we report 285 compact sources, or 816 in the high completeness catalog. These sources have effective radii between 0.04-0.4 pc, and are the potential progenitors of star clusters. The masses for both catalogs are dominated by the Sagittarius B2 cloud complex, where masses are likely unreliable due to free-free contamination, uncertain dust temperatures, and line-of-sight confusion. Given the survey selection and completeness, we predict that our robust catalog accounts for more than ~99% of compact substructure capable of forming high mass stars in the CMZ. This catalog provides a crucial foundation for future studies of high-mass star formation in the Milky Way's Galactic Center.

astro-ph.GA↗

arXiv2020

CMZoom: Survey Overview and First Data Release

We present an overview of the CMZoom survey and its first data release. CMZoom is the first blind, high-resolution survey of the Central Molecular Zone (CMZ; the inner 500 pc of the Milky Way) at wavelengths sensitive to the pre-cursors of high-mass stars. CMZoom is a 500-hour Large Program on the Submillimeter Array (SMA) that mapped at 1.3 mm all of the gas and dust in the CMZ above a molecular hydrogen column density of 10^23 cm^-2 at a resolution of ~3" (0.1 pc). In this paper, we focus on the 1.3 mm dust continuum and its data release, but also describe CMZoom spectral line data which will be released in a forthcoming publication. While CMZoom detected many regions with rich and complex substructure, its key result is an overall deficit in compact substructures on 0.1 - 2 pc scales (the compact dense gas fraction: CDGF). In comparison with clouds in the Galactic disk, the CDGF in the CMZ is substantially lower, despite having much higher average column densities. CMZ clouds with high CDGFs are well-known sites of active star formation. The inability of most gas in the CMZ to form compact substructures is likely responsible for the dearth of star formation in the CMZ, surprising considering its high density. The factors responsible for the low CDGF are not yet understood but are plausibly due to the extreme environment of the CMZ, having far-reaching ramifications for our understanding of the star formation process across the cosmos.

astro-ph.GA↗

arXiv2020

The MUSTANG-2 Galactic Plane Survey (MGPS90) pilot

We report the results of a pilot program for a Green Bank Telescope (GBT) MUSTANG Galactic Plane survey at 3 mm (90 GHz), MGPS90. The survey achieves a typical $1σ$ depth of $1-2$ mJy beam$^{-1}$ with a 9" beam. We describe the survey parameters, quality assessment process, cataloging, and comparison with other data sets. We have identified 709 sources over seven observed fields selecting some of the most prominent millimeter-bright regions between $0°< \ell < 50°$ (total area $\approx 7.5 °^2$). The majority of these sources have counterparts at other wavelengths. By applying flux selection criteria to these sources, we successfully recovered several known hypercompact HII (HCHII) regions, but did not confirm any new ones. We identify 126 sources that have mm-wavelength counterparts but do not have cm-wavelength counterparts and are therefore candidate HCHII regions; of these, 10 are morphologically compact and are strong candidates for new HCHII regions. Given the limited number of candidates in the extended area in this survey compared to the relatively large numbers seen in protoclusters W51 and W49, it appears that most HCHII regions exist within dense protoclusters. Comparing the counts of HCHII to ultracompact HII (UCHII) regions, we infer the HCHII region lifetime is 16-46% that of the UCHII region lifetime. We additionally separated the 3 mm emission into dust and free-free emission by comparing with archival 870 $μ$m and 20 cm data. In the selected pilot fields, most ($\gtrsim80$%) of the 3 mm emission comes from plasma, either through free-free or synchrotron emission.

astro-ph.GA↗

arXiv2019

6.7 GHz CH3OH absorption towards the N3 Galactic Center point-source

We present evidence of 6.7 GHz methanol (CH3OH)~and 4.8 GHz formaldehyde (H2CO) absorption towards the Galactic Center (GC) point-source `N3'. Both absorption features are unresolved and spatially aligned with N3. The 6.7 GHz CH3OH contains a single velocity component (centered at ~10 km/s) while the 4.8 GHz H2CO shows two velocity components (centered at ~-3 and +8 km/s). We find that the velocity of these absorption components are similar to that of emission lines from other molecules (e.g., SiO and H3CN) detected toward this compact-source (-13 to +25 km/s; `N3 cloud'). The detection of these absorption features is a firm indication that some of the molecular gas in the N3 molecular cloud is on the near-side of the continuum source. Analysis of the CH3OH absorption kinematics shows a relatively large velocity dispersion (3.8 km/s) for the size scale of this feature (<0.1'', <0.01 pc at the GC; Ludovici et al. 2016), when compared with other similar size GC clouds in the Larson linewidth-size relationship. Further, this linewidth is closer to velocity dispersion measurements for size scales of 1.3 pc, which is roughly the width of the N3 cloud (25''; 1.0 pc). We argue that this relatively broad linewidth, over a small cross-sectional area, is due to turbulence through the depth of the cloud, where the cloud has a presumed line-of-sight thickness of ~1 pc.

astro-ph.GA↗

arXiv2019

A Census of Early Phase High-Mass Star Formation in the Central Molecular Zone

We present new observations of C-band continuum emission and masers to assess high-mass ($>$8 $M_\odot$) star formation at early evolutionary phases in the inner 200 pc of the Central Molecular Zone (CMZ) of the Galaxy. The continuum observation is complete to free-free emission from stars above 10-11 $M_\odot$ in 91% of the covered area. We identify 104 compact sources in the continuum emission, among which five are confirmed ultracompact H II regions, 12 are candidates of ultra-compact H II regions, and the remaining 87 sources are mostly massive stars in clusters, field stars, evolved stars, pulsars, extragalactic sources, or of unknown nature that is to be investigated. We detect class II CH$_3$OH masers at 23 positions, among which six are new detections. We confirm six known H$_2$CO masers in two high-mass star forming regions, and detect two new H$_2$CO masers toward the Sgr C cloud, making it the ninth region in the Galaxy that contains masers of this type. In spite of these detections, we find that current high-mass star formation in the inner CMZ is only taking place in seven isolated clouds. The results suggest that star formation at early evolutionary phases in the CMZ is about 10 times less efficient than expected by the dense gas star formation relation, which is in line with previous studies that focus on more evolved phases of star formation. This means that if there will be any impending, next burst of star formation in the CMZ, it has not yet begun.

astro-ph.GA↗

arXiv2017

M0.20-0.033: An Expanding Molecular Shell in the Galactic Center Radio Arc

We present high-frequency Karl G. Jansky Very Large Array (VLA) continuum and spectral line (NH3, H64$α$, and H63$α$) observations of the Galactic Center Radio Arc region, covering the Sickle H II region, the Quintuplet cluster, and molecular clouds M0.20-0.033 and M0.10-0.08. These observations show that the two velocity components of M0.20-0.033 (~25 & 80 km/s), previously thought to be separate clouds along the same line-of-sight, are physically connected in position-velocity space via a third southern component around 50 km/s. Further position-velocity analysis of the surrounding region, using lower-resolution survey observations taken with the Mopra and ATCA telescopes, indicates that both molecular components in M0.20-0.033 are physically connected to the M0.10-0.08 molecular cloud, which is suggested to be located on stream 1 in the Kruijssen et al. (2015) orbital model. The morphology and kinematics of the molecular gas in M0.20-0.033 indicate that the two velocity components in M0.20-0.033 constitute an expanding shell. Our observations suggest that the M0.20-0.033 expanding shell has an expansion velocity of 40 km/s, with a systemic velocity of 53 km/s, comparable to velocities detected in M0.10-0.08. The origin of the expanding shell is located near the Quintuplet cluster, suggesting that the energy and momentum output from this massive stellar cluster may have contributed to the expansion.

astro-ph.GA↗

arXiv2013

The Optical Green Valley vs Mid-IR Canyon in Compact Groups

Compact groups of galaxies provide conditions similar to those experienced by galaxies in the earlier universe. Recent work on compact groups has led to the discovery of a dearth of mid-infrared transition galaxies (MIRTGs) in IRAC (3.6 - 8.0 micron) color space (Johnson et al. 2007; Walker et al. 2012) as well as at intermediate specific star formation rates (Tzanavaris et al. 2010). However, we find that in compact groups these mid-infrared (mid-IR) transition galaxies in the mid-infrared dearth have already transitioned to the optical ([g-r]) red sequence. We investigate the optical color-magnitude diagram (CMD) of 99 compact groups containing 348 galaxies and compare the optical CMD with mid-IR color space for compact group galaxies. Utilizing redshifts available from SDSS, we identified new galaxy members for 6 groups. By combining optical and mid-IR data, we obtain information on both the dust and the stellar populations in compact group galaxies. We also compare with more isolated galaxies and galaxies in the Coma cluster, which reveals that, similar to clusters, compact groups are dominated by optically red galaxies. While we find that compact group transition galaxies lie on the optical red sequence, LVL+SINGS mid-IR transition galaxies span the range of optical colors. The dearth of mid-IR transition galaxies in compact groups may be due to a lack of moderately star forming low mass galaxies; the relative lack of these galaxies could be due to their relatively small gravitational potential wells. This makes them more susceptible to this dynamic environment, thus causing them to more easily lose gas or be accreted by larger members.

astro-ph.CO↗