arXiv subjects

E. Bergin

Publications and source records attributed to E. Bergin.

At least 19 recordsLinked to original sources

arXiv2025

Direct Measurement of Extinction in a Planet-Hosting Gap

Recent disk observations have revealed multiple indirect signatures of forming gas giant planets, but high-contrast imaging has rarely confirmed the presence of the suspected perturbers. Here, we exploit a unique opportunity provided by the background star AS209bkg, which shines through a wide annular gap in the AS209 disk, to perform transmission spectrophotometry and directly measure the extinction from gap material for the first time. By combining new VLT/SPHERE and JWST/NIRCam observations with archival HST data from 2005, we model the spectral energy distribution (SED) of AS209bkg over a 19-year baseline. We find that the SED and its variability are best explained by increasing extinction along the line of sight as AS209bkg approaches the gap edge in projection. The extinction is best described by a combination of ISM-like extinction component and a grey extinction component. This points to the presence of grains in the disk outer gap that are larger than in the ISM. We find that the extinction in the gap at $\lambda\sim4.0~\mu$m is $A_{4\,\mu\mathrm{m}} = 2.7^{+0.7}_{-0.7}$ mag, while at H$\alpha$ ($\lambda=0.656~\mu$m), where most searches for accretion signatures take place, the extinction could be as high as $A_\mathrm{H\alpha} = 4.2^{+0.9}_{-1.2}$ mag ($A_V=4.6^{+1.0}_{-1.3}$ mag). This suggests that even wide, deep gaps can significantly obscure emission from protoplanets, even those following a hot-start evolutionary model. Our extinction measurements help reconcile the discrepancy between ALMA-based predictions of planet-disk interactions and the non-detections from sensitive optical and near-infrared imaging campaigns.

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arXiv2022

MIRAC-5: A ground-based mid-IR instrumentwith the potential to detect ammonia in gas giants

We present the fifth incarnation of the Mid-Infrared Array Camera (MIRAC-5) instrument which will use a new GeoSnap (3 - 13 microns) detector. Advances in adaptive optics (AO) systems and detectors are enabling ground-based mid-infrared systems capable of high spatial resolution and deep contrast. As one of the only 3 - 13 micron cameras used in tandem with AO, MIRAC-5 will be complementary to the James Webb Space Telescope (JWST) and capable of characterizing gas giant exoplanets and imaging forming protoplanets (helping to characterize their circumplanetary disks). We describe key features of the MIRAC-5 GeoSnap detector, a long-wave Mercury-Cadmium-Telluride (MCT) array produced by Teledyne Imaging Sensors (TIS), including its high quantum efficiency (> 65%), large well-depth, and low noise. We summarize MIRAC-5's important capabilities, including prospects for obtaining the first continuum mid-infrared measurements for several gas giants and the first 10.2-10.8 micron NH3 detection in the atmosphere of the warm companion GJ 504b (Teff ~550 K) within 8 hours of observing time. Finally, we describe plans for future upgrades to MIRAC-5 such as adding a coronagraph. MIRAC-5 will be commissioned on the MMT utilizing the new MAPS AO system in late 2022 with plans to move to Magellan with the MagAO system in the future.

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arXiv2021

MOSAIC on the ELT: high-multiplex spectroscopy to unravel the physics of stars and galaxies from the dark ages to the present-day

The powerful combination of the cutting-edge multi-object spectrograph MOSAIC with the world largest telescope, the ELT, will allow us to probe deeper into the Universe than was possible. MOSAIC is an extremely efficient instrument in providing spectra for the numerous faint sources in the Universe, including the very first galaxies and sources of cosmic reionization. MOSAIC has a high multiplex in the NIR and in the VIS, in addition to multi-Integral Field Units (Multi-IFUs) in NIR. As such it is perfectly suited to carry out an inventory of dark matter (from rotation curves) and baryons in the cool-warm gas phases in galactic haloes at z=3-4. MOSAIC will enable detailed maps of the intergalactic medium at z=3, the evolutionary history of dwarf galaxies during a Hubble time, the chemistry directly measured from stars up to several Mpc. Finally, it will measure all faint features seen in cluster gravitational lenses or in streams surrounding nearby galactic halos, providing MOSAIC to be a powerful instrument with an extremely large space of discoveries. The preliminary design of MOSAIC is expected to begin next year, and its level of readiness is already high, given the instrumental studies made by the team.

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arXiv2019

Origins Space Telescope Mission Concept Study Report

The Origins Space Telescope (Origins) traces our cosmic history, from the formation of the first galaxies and the rise of metals to the development of habitable worlds and present-day life. Origins does this through exquisite sensitivity to infrared radiation from ions, atoms, molecules, dust, water vapor and ice, and observations of extra-solar planetary atmospheres, protoplanetary disks, and large-area extragalactic fields. Origins operates in the wavelength range 2.8 to 588 microns and is 1000 times more sensitive than its predecessors due to its large, cold (4.5 K) telescope and advanced instruments. Origins was one of four large missions studied by the community with support from NASA and industry in preparation for the 2020 Decadal Survey in Astrophysics. This is the final study report.

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arXiv2019

The complexity of Orion: an ALMA view III. The explosion impact

The chemistry of complex organic molecules in interstellar dark clouds is still highly uncertain in part because of the lack of constraining observations. Orion is the closest massive star-forming region, and observations making use of ALMA allow us to separate the emission regions of various complex organic molecules (COMs) in both velocity and space. Orion also benefits from an exceptional situation, in that it is the site of a powerful explosive event that occurred 550 years ago. We show that the closely surrounding Kleinmann-Low region has clearly been influenced by this explosion; some molecular species have been pushed away from the densest parts while others have remained in close proximity. This dynamical segregation reveals the time dependence of the chemistry and, therefore allows us to better constrain the formation sequence of COMs and other species, including deuterated molecules.

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arXiv2017

Large turbulent reservoirs of cold molecular gas around high-redshift starburst galaxies

Starburst galaxies at the peak of cosmic star formation are among the most extreme starforming engines in the universe, producing stars over ~100 Myr. The star formation rates of these galaxies, which exceed 100 $M_\odot$ per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Starburst galaxies are therefore ideal targets to unravel the critical interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH$^+$, is a most useful molecule for such studies because it cannot form in cold gas without supra-thermal energy input, so its presence highlights dissipation of mechanical energy or strong UV irradiation. Here, we report the detection of CH$^+$(J=1-0) emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts z~2.5. This line has such a high critical density for excitation that it is emitted only in very dense ($>10^5$ cm$^{-3}$) gas, and is absorbed in low-density gas. We find that the CH$^+$ emission lines, which are broader than 1000 km s$^{-1}$, originate in dense shock waves powered by hot galactic winds. The CH$^+$ absorption lines reveal highly turbulent reservoirs of cool ($T\sim 100$K), low-density gas, extending far outside (>10 kpc) the starburst cores (radii <1 kpc). We show that the galactic winds sustain turbulence in the 10 kpc-scale environments of the starburst cores, processing these environments into multi-phase, gravitationally bound reservoirs. However, the mass outflow rates are found to be insufficient to balance the star formation rates. Another mass input is therefore required for these reservoirs, which could be provided by on-going mergers or cold stream accretion. Our results suggest that galactic feedback, coupled jointly to turbulence and gravity, extends the starburst phase instead of quenching it.

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arXiv2017

The physical and chemical structure of Sagittarius B2. II. Continuum millimeter emission of SgrB2(M) and SgrB2(N) with ALMA

The high-mass star forming sites SgrB2(M) and SgrB2(N) have been the target of numerous studies, revealing e.g. a rich chemistry. We want to characterize their physical and chemical structure using ALMA high-angular resolution observations at mm wavelengths, reaching spatial scales of about 4000 au, and covering the whole band 6 (from 211 to 275 GHz). In order to determine the continuum emission in line-rich sources, we use a new statistical method: STATCONT. We detect 27 continuum sources in SgrB2(M) and 20 in SgrB2(N). We study the continuum emission across the ALMA band 6, and compare it with previous SMA 345 GHz and VLA 40 GHz observations, to study the nature of the sources detected. The brightest sources are dominated by (partially optically thick) dust emission, while there is an important degree of contamination from ionized gas free-free emission in weaker sources. While the total mass in SgrB2(M) is distributed in many fragments, most of the mass in SgrB2(N) arises from a single object, with filamentary-like structures converging towards the center. There seems to be a lack of low-mass dense cores in both regions. We determine H2 volume densities for the cores of about 10^5-10^7 Msun pc^-3, one to two orders of magnitude higher than the stellar densities of super star clusters. In general, SgrB2(N) is chemically richer than SgrB2(M). There seems to be a correlation between the chemical richness and the mass of the fragments, with more massive clumps being more chemically rich. Both SgrB2(N) and SgrB2(M) harbour a cluster of hot molecular cores. We compare the continuum images with predictions from a detailed 3D radiative transfer model that reproduces the structure of SgrB2 from 45 pc down to 100 au. This dataset, together with ongoing projects in the range 5 to 200 GHz, better constrain the 3D structure of SgrB2, and allow us to understand its physical and chemical structure.

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arXiv2016

The Far-Infrared Surveyor Mission Study: Paper I, the Genesis

This paper describes the beginning of the Far-Infrared Surveyor mission study for NASA's Astrophysics Decadal 2020. We describe the scope of the study, and the open process approach of the Science and Technology Definition Team. We are currently developing the science cases and provide some preliminary highlights here. We note key areas for technological innovation and improvements necessary to make a Far-Infrared Surveyor mission a reality.

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arXiv2016

Probing the CO and methanol snow lines in young protostars. Results from the CALYPSO IRAM-PdBI survey

Context. "Snow lines", marking regions where abundant volatiles freeze out onto the surface of dust grains, play an important role for planet growth and bulk composition in protoplanetary disks. They can already be observed in the envelopes of the much younger, low-mass Class 0 protostars that are still in their early phase of heavy accretion. Aims. We aim at using the information on the sublimation regions of different kinds of ices to understand the chemistry of the envelope, its temperature and density structure, and the history of the accretion process. Methods. As part of the CALYPSO IRAM Large Program, we have obtained observations of C$^{18}$O, N$_2$H$^+$ and CH$_3$OH towards nearby Class 0 protostars with the IRAM Plateau de Bure interferometer at sub-arcsecond resolution. For four of these sources we have modeled the emission using a chemical code coupled with a radiative transfer module. Results. We observe an anti-correlation of C$^{18}$O and N$_2$H$^+$ in NGC 1333-IRAS4A, NGC 1333-IRAS4B, L1157, and L1448C, with N$_2$H$^+$ forming a ring around the centrally peaked C$^{18}$O emission due to N$_2$H$^+$ being chemically destroyed by CO. The emission regions of models and observations match for a CO binding energy of 1200 K, which is higher than the binding energy of pure CO ices ($\sim$855 K). Furthermore, we find very low CO abundances inside the snow lines in our sources, about an order of magnitude lower than the total CO abundance observed in the gas on large scales in molecular clouds before depletion sets in. Conclusions. The high CO binding energy may hint at CO being frozen out in a polar ice environment like amorphous water ice or in non-polar CO$_2$-rich ice. The low CO abundances are comparable to values found in protoplanetary disks, which may indicate an evolutionary scenario where these low values are already established in the protostellar phase. (Abbr. Version)

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arXiv2016

The physical and chemical structure of Sagittarius B2, I. Three-dimensional thermal dust and free-free continuum modeling on 100 au to 45 pc scales

We model the dust and free-free continuum emission in the high-mass star-forming region Sagittarius B2 in order to reconstruct the three-dimensional density and dust temperature distribution, as a crucial input to follow-up studies of the gas velocity field and molecular abundances. We employ the three-dimensional radiative transfer program RADMC-3D to calculate the dust temperature self-consistently, provided a given initial density distribution. This density distribution of the entire cloud complex is then recursively reconstructed based on available continuum maps, including both single-dish and high-resolution interferometric maps covering a wide frequency range (40 GHz - 4 THz). The model covers spatial scales from 45 pc down to 100 au, i.e. a spatial dynamic range of 10^5. We find that the density distribution of Sagittarius B2 can be reasonably well fitted by applying a superposition of spherical cores with Plummer-like density profiles. In order to reproduce the spectral energy distribution, we position Sgr B2(N) along the line of sight behind the plane containing Sgr B2(M). We find that the entire cloud complex comprises a total gas mass of 8.0 x 10^6 Msun within a diameter of 45 pc, corresponding to an averaged gas density of 170 Msun/pc^3. We estimate stellar masses of 2400 Msun and 20700 Msun and luminosities of 1.8 x 10^6 Lsun and 1.2 x 10^7 Lsun for Sgr B2(N) and Sgr B2(M), respectively. We report H_2 column densities of 2.9 x 10^24 cm^-2 for Sgr B2(N) and 2.5 x 10^24 cm^-2 for Sgr B2(M) in a 40" beam. For Sgr B2(S), we derive a stellar mass of 1100 Msun, a luminosity of 6.6 x 10^5 Lsun and a H_2 column density of 2.2 x 10^24 cm^-2 in a 40" beam. We calculate a star formation efficiency of 5% for Sgr B2(N) and 50% for Sgr B2(M), indicating that most of the gas content in Sgr B2(M) has already been converted to stars or dispersed.

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arXiv2015

A Cryogenic Space Telescope for Far-Infrared Astrophysics: A Vision for NASA in the 2020 Decade

Many of the transformative processes in the Universe have taken place in regions obscured by dust, and are best studied with far-IR spectroscopy. We present the Cryogenic-Aperture Large Infrared-Submillimeter Telescope Observatory (CALISTO), a 5-meter class, space-borne telescope actively cooled to 4 K, emphasizing moderate-resolution spectroscopy in the crucial 35 to 600 micron band. CALISTO will enable NASA and the world to study the rise of heavy elements in the Universe's first billion years, chart star formation and black hole growth in dust-obscured galaxies through cosmic time, and conduct a census of forming planetary systems in our region of the Galaxy. CALISTO will capitalize on rapid progress in both format and sensitivity of far-IR detectors. Arrays with a total count of a few 100,000 detector pixels will form the heart of a suite of imaging spectrometers in which each detector reaches the photon background limit. This document contains a large overview paper on CALISTO, as well as six 2-3 page scientific white papers, all prepared in response to NASA's Cosmic Origins Program Analysis Group (COPAG's) request for input on future mission concepts. The Far-IR Science Interest Group will meet from 3-5 June 2015 with the intention of reaching consensus on the architecture for the Far-IR Surveyor mission. This white paper describes one of the architectures to be considered by the community. One or more companion papers will describe alternative architectures.

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arXiv2014

Detections of trans-Neptunian ice in protoplanetary disks

We present Herschel Space Observatory PACS spectra of T Tauri stars, in which we detect amorphous and crystalline water ice features. Using irradiated accretion disk models, we determine the disk structure and ice abundance in each of the systems. Combining a model-independent comparison of the ice feature strength and disk size with a detailed analysis of the model ice location, we estimate that the ice emitting region is at disk radii >30AU, consistent with a proto-Kuiper belt. Vertically, the ice emits most below the photodesorption zone, consistent with Herschel observations of cold water vapor. The presence of crystallized water ice at a disk location a) colder than its crystallization temperature and b) where it should have been re-amorphized in ~1 Myr suggests that localized generation is occurring; the most likely cause appears to be micrometeorite impact or planetesimal collisions. Based on simple tests with UV models and different ice distributions, we suggest that the SED shape from 20 to 50 micron may probe the location of the water ice snow line in the disk upper layers. This project represents one of the first extra-solar probes of the spatial structure of the cometary ice reservoir thought to deliver water to terrestrial planets.

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arXiv2014

Atomic jet from SMM1 (FIRS1) in Serpens uncovers non-coeval binary companion

We report on the detection of an atomic jet associated with the protostellar source SMM1 (FIRS1) in Serpens. The jet is revealed in [FeII] and [NeII] line maps observed with Spitzer/IRS, and further confirmed in HiRes IRAC and MIPS images. It is traced very close to SMM1 and peaks at ~5 arcsec" from the source at a position angle of $\sim 125 degrees. In contrast, molecular hydrogen emission becomes prominent at distances > 5" from the protostar and extends at a position angle of 160 degrees. The morphological differences suggest that the atomic emission arises from a companion source, lying in the foreground of the envelope surrounding the embedded protostar SMM1. In addition the molecular and atomic Spitzer maps disentangle the large scale CO (3-2) emission observed in the region into two distinct bipolar outflows, giving further support to a proto-binary source setup. Analysis at the peaks of the [FeII] jet show that emission arises from warm and dense gas (T ~1000 K, n(electron) 10^5 - 10^6 cm^-3). The mass flux of the jet derived independently for the [FeII] and [NeII] lines is 10^7 M(sun)/yr, pointing to a more evolved Class~I/II protostar as the driving source. All existing evidence converge to the conclusion that SMM1 is a non-coeval proto-binary source.

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arXiv2013

Water in star forming regions with Herschel (WISH) III. Far-infrared cooling lines in low-mass young stellar objects

(Abridged) Far-infrared Herschel-PACS spectra of 18 low-mass protostars of various luminosities and evolutionary stages are studied. We quantify their far-infrared line emission and the contribution of different atomic and molecular species to the gas cooling budget during protostellar evolution. We also determine the spatial extent of the emission and investigate the underlying excitation conditions. Most of the protostars in our sample show strong atomic and molecular far-infrared emission. Water is detected in 17 objects, including 5 Class I sources. The high-excitation H2O line at 63.3 micron is detected in 7 sources. CO transitions from J=14-13 up to 49-48 are found and show two distinct temperature components on Boltzmann diagrams with rotational temperatures of ~350 K and ~700 K. H2O has typical excitation temperatures of ~150 K. Emission from both Class 0 and I sources is usually spatially extended along the outflow direction but with a pattern depending on the species and the transition. The H2O line fluxes correlate strongly with those of the high-J CO lines, as well as with the bolometric luminosity and envelope mass. They correlate less strongly with OH and not with [OI] fluxes. The PACS data probe at least two physical components. The H2O and CO emission likely arises in non-dissociative (irradiated) shocks along the outflow walls with a range of pre-shock densities. Some OH is also associated with this component, likely resulting from H2O photodissociation. UV-heated gas contributes only a minor fraction to the CO emission observed by PACS, based on the strong correlation between the shock-dominated CO 24-23 line and the CO 14-13 line. [OI] and some of the OH emission probe dissociative shocks in the inner envelope. The total far-infrared cooling is dominated by H2O and CO, with [OI] increasing for Class I sources.

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arXiv2012

Herschel/HIFI observations of [CII] and [13CII] in PDRs

Recently, we introduced detailed isotopic chemistry into the KOSMA-tau model for photon-dominated regions (PDRs) to give theoretical predictions for the abundance of the carbon isotopologues as a function of PDR parameters. Combined with radiative transfer computations for specific geometries, we estimated the possible intensity ratio of the [CII]/[13CII] lines. Here, we compare these predictions with new observations. We performed Herschel/HIFI observations of the [CII] 158micron line in a number of PDRs. In all sources we observed at least two hyperfine components of the [13CII] transition allowing to determine the [CII]/[13CII] intensity ratio, after some revision of the intrinsic hyperfine ratios. Comparing the intensity ratios with the results from the updated KOSMA-tau model, we identify cases dominated by chemical fractionation and cases dominated by the optical depth of the main isotopic line. An observable enhancement of the [CII]/[13CII] intensity ratio due to chemical fractionation depends mostly on geometry and velocity structure, and less on the gas density and radiation field. In our observations the [CII]/[13CII] ratio for the integrated line intensity was always dominated by the optical depth of the main isotopic line. However, an enhanced intensity ratio is found for particular velocity components in a few sources: the red-shifted material in the ultracompact HII region Mon R2, the wings of the turbulent profile in the Orion Bar, and possibly a blue wing in NGC7023. The mapping of the [13CII] lines in the Orion Bar allows to derive a C+ column density map confirming the temperature stratification of the C+ layer, in agreement with the chemical stratification of the Bar. The C+ column densities for all sources show that at the position of the [CII] peak emission, a dominant fraction of the gas-phase carbon is in the form of C+.

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arXiv2012

Tracing High-Energy Radiation from T Tauri Stars Using Mid-Infrared Neon Emission from Disks

High-energy radiation from T Tauri stars (TTS) influences the amount and longevity of gas in disks, thereby playing a crucial role in the creation of gas giant planets. Here we probe the high-energy ionizing radiation from TTS using high-resolution mid-infrared (MIR) Spitzer IRS Neon forbidden line detections in a sample of disks from IC 348, NGC 2068, and Chamaeleon. We report three new detections of [Ne III] from CS Cha, SZ Cha, and T 54, doubling the known number of [Ne III] detections from TTS. Using [Ne III]-to-[Ne II] ratios in conjunction with X-ray emission measurements, we probe high-energy radiation from TTS. The majority of previously inferred [Ne III]/[Ne II] ratios based on [Ne III] line upper limits are significantly less than 1, pointing to the dominance of either X-ray radiation or soft Extreme-Ultraviolet (EUV) radiation in producing these lines. Here we report the first observational evidence for hard EUV dominated Ne forbidden line production in a T Tauri disk: [Ne III]/[Ne II]~1 in SZ Cha. Our results provide a unique insight into the EUV emission from TTS, by suggesting that EUV radiation may dominate the creation of Ne forbidden lines, albeit in a minority of cases.

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arXiv2011

The unusual protoplanetary disk around the T Tauri star ET Cha

We present new continuum and line observations, along with modelling, of the faint (6-8) Myr old T Tauri star ET Cha belonging to the eta Chamaeleontis cluster. We have acquired HERSCHEL/PACS photometric fluxes at 70 mic and 160 mic, as well as a detection of the [OI] 63 mic fine-structure line in emission, and derived upper limits for some other far-IR OI, CII, CO and o-H2O lines. The HERSCHEL data is complemented by new ANDICAM B-K photometry, new HST/COS and HST/STIS UV-observations, a non-detection of CO J=3-2 with APEX, re-analysis of a UCLES high-resolution optical spectrum showing forbidden emission lines like [OI] 6300A, [SII] 6731A and 6716A, and [NII] 6583A, and a compilation of existing broad-band photometric data. We used the thermo-chemical disk code ProDiMo and the Monte-Carlo radiative transfer code MCFOST to model the protoplanetary disk around ET Cha. Based on these models we can determine the disk dust mass Mdust = (2.E-8 - 5.E-8) Msun, whereas the total disk gas mass is found to be only little constrained, Mgas = (5.E-5 - 3.E-3) Msun. In the models, the disk extends from 0.022 AU (just outside of the co-rotation radius) to only about 10 AU. Larger disks are found to be inconsistent with the CO J=3-2 non-detection. The low velocity component of the [OI] 6300A emission line is consistent with being emitted from the inner disk. The model can also reproduce the line flux of H2 v=1-0 S(1) at 2.122 mic. An additional high-velocity component of the [OI] 6300A emission line, however, points to the existence of an additional jet/outflow of low velocity (40 - 65) km/s with mass loss rate ~1.E-9 Msun/yr. In relation to our low estimations of the disk mass, such a mass loss rate suggests a disk lifetime of only ~(0.05 - 3) Myr, substantially shorter than the cluster age. The evolutionary state of this unusual protoplanetary disk is discussed.

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arXiv2010

GGD 37: An Extreme Protostellar Outflow

We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne V]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne V] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s-1. The presence of an extended pho- toionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.

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