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Introduction
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Education
September 2001 - December 2003
September 2000 - August 2001
Publications
Publications (231)
Context . The Cygnus-X complex is a massive (a few 10 ⁶ M ⊙ molecular gas mass), nearby (1.4 kpc) star-forming region with several OB associations. Of these, Cyg OB2 is the largest, with at least 169 OB stars. DR18 is the largest globule near the OB2 association, making it a perfect target for investigating the influence of ultraviolet radiation on...
The Cygnus-X complex is a massive, nearby (1.4 kpc) star-forming region with several OB associations. As part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program, we carried out 3.6 millimeter (mm) continuum and spectral line high-resolution observations ($\sim$ 3 - 4$''$) toward DR18, covering several molecular...
Context. Theoretical models of early accretion during the formation process of massive stars have predicted that H II regions exhibit radio variability on timescales of decades. However, large-scale searches for such temporal variations with sufficient sensitivity have not yet been carried out.
Aims. Our aim is to identify H II regions with variabl...
Context: Theoretical models of early accretion during the formation process of massive stars have predicted that HII regions exhibit radio variability on timescales of decades. However, large-scale searches for such temporal variations with sufficient sensitivity have not yet been carried out. Aims: We aim to identify HII regions with variable radi...
Context. The GLObal view on STAR formation in the Milky Way (GLOSTAR) survey studies star formation with the Very Large Array (VLA) and the Effelsberg 100 meter radio telescope in the Galactic plane between −2° < ℓ < 60° and | b | < 1°, and the Cygnus X region (76° < ℓ < 83° and −1° < b < 2°), with unprecedented sensitivity in both flux density (1...
Studies of Galactic H ii regions are of crucial importance for studying star formation and the evolution of the interstellar medium. Gaining an insight into their physical characteristics contributes to a more comprehensive understanding of these phenomena. The GLOSTAR project aims to provide a GLObal view on STAR formation in the Milky Way by perf...
The GLOSTAR survey studies star formation with the VLA and the Effelsberg 100m telescope in the Galactic plane (-2d<l<60d; |b|<1d) and the Cygnus X region with unprecedented sensitivity in both flux density (~50uJy/beam) and the capability of detecting emission with angular scales in the range from 1" to the largest radio structures in the Galaxy....
Studies of Galactic HII regions are of crucial importance for studying star formation and the evolution of the interstellar medium. Gaining an insight into their physical characteristics contributes to a more comprehensive understanding of these phenomena. The GLOSTAR project aims to provide a GLObal view on STAR formation in the Milky Way by perfo...
We report measurements of trigonometric parallax and proper motion for two 6.7 GHz methanol and two 22 GHz water masers located in the far portion of the Sagittarius spiral arm as part of the BeSSeL Survey. Distances for these sources are estimated from parallax measurements combined with 3-dimensional kinematic distances. The distances of G033.64$...
We report measurements of trigonometric parallax and proper motion for two 6.7 GHz methanol and two 22 GHz water masers located in the far portion of the Sagittarius spiral arm as part of the BeSSeL Survey. Distances for these sources are estimated from parallax measurements combined with three-dimensional kinematic distances. The distances of G033...
We present the results of a search for ammonia maser emission in 119 Galactic high-mass star-forming regions (HMSFRs) known to host 22\,GHz H$_2$O maser emission. Our survey has led to the discovery of non-metastable NH$_3$ inversion line masers toward 14 of these sources. This doubles the number of known non-metastable ammonia masers in our Galaxy...
As part of the GLObal view of STAR formation in the Milky Way (GLOSTAR) survey, we present the high-resolution continuum source catalog for the regions ( ℓ = 2° −28°, 36° −40°, 56° −60°, and | b | < 1.0°), observed with the Karl G. Jansky Very Large Array (VLA) in its B-configuration. The continuum images were optimized to detect compact sources on...
Context . Stars form in the dense interiors of molecular clouds. The dynamics and physical properties of the atomic interstellar medium (ISM) set the conditions under which molecular clouds and eventually stars form. It is, therefore, critical to investigate the relationship between the atomic and molecular gas phase to understand the global star f...
Context. The advent of wide-band receiver systems on interferometer arrays has enabled the undertaking of high-sensitivity and highresolution radio continuum surveys of the Galactic plane in a reasonable amount of telescope time. Yet, to date, there have been only a few such studies of the first quadrant of the Milky Way carried out at frequencies...
Context. Cygnus X is one of the closest and most active high-mass star-forming regions in our Galaxy, making it one of the best laboratories for studying massive star formation.
Aims. We aim to investigate the properties of molecular gas structures on different linear scales with the 4.8 GHz formaldehyde (H 2 CO) absorption line in Cygnus X.
Method...
Cygnus X is one of the closest and most active high-mass star-forming regions in our Galaxy, making it one of the best laboratories for studying massive star formation. As part of the GLOSTAR Galactic plane survey, we performed large scale simultaneous H$_{2}$CO (1$_{1,0}$-1$_{1,1}$) spectral line and radio continuum imaging observations toward Cyg...
We present the first results from the Southern Hemisphere Parallax Interferometric Radio Astrometry Legacy Survey: 10 μ as accurate parallaxes and proper motions for two Southern Hemisphere 6.7 GHz methanol masers obtained using the inverse MultiView calibration method. Using an array of radio telescopes in Australia and New Zealand, we measured tr...
Galactic plane radio surveys play a key role in improving our understanding of a wide range of astrophysical phenomena. Performing such a survey using the latest interferometric telescopes produces large data rates necessitating a shift towards fully or quasi-real-time data analysis with data being stored for only the time required to process them....
Galactic plane radio surveys play a key role in improving our understanding of a wide range of astrophysical phenomena from neutron stars and Galactic magnetic fields to stellar formation and evolution. Performing such a survey on the latest interferometric telescopes produces large data rates necessitating a shift towards fully or quasi-real-time...
Context. While over 1000 supernova remnants (SNRs) are estimated to exist in the Milky Way, only less than 400 have been found to date. In the context of this apparent deficiency, more than 150 SNR candidates were recently identified in the D-configuration Very Large Array (VLA-D) continuum images of the 4–8 GHz global view on star formation (GLOST...
As part of the Global View on Star Formation (GLOSTAR) survey we have used the Karl G. Jansky Very Large Array (VLA) in its B-configuration to observe the part of the Galactic plane between longitudes of 28° and 36° and latitudes from −1° to +1° at the C -band (4–8 GHz). To reduce the contamination of extended sources that are not well recovered by...
Context. While over 1000 supernova remnants (SNRs) are estimated to exist in the Milky Way, only less than 400 have been found to date. In the context of this apparent deficiency, more than 150 SNR candidates were recently identified in the D-configuration Very Large Array (VLA-D) continuum images of the 4--8 GHz global view on star formation (GLOS...
Studying the interplay between massive star formation and the interstellar medium (ISM) is paramount to understand the evolution of galaxies. Radio continuum (RC) emission serves as an extinction-free tracer of both massive star formation and the energetic components of the ISM. We present a multiband RC survey of the Local Group galaxy M 33 down t...
We present extensive multifrequency Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) observations of the radio-bright supernova (SN) IIb SN 2004C that span ∼40–2793 days post-explosion. We interpret the temporal evolution of the radio spectral energy distribution in the context of synchrotron self-absorbed emission from the...
As part of the GLOSTAR survey we have used the VLA in its B-configuration to observe the part of the Galactic plane between longitudes of 28d and 36d and latitudes from -1d to +1d at the C-band (4--8 GHz). To reduce the contamination of extended sources that are not well recovered by our coverage of the (u, v)-plane we discarded short baselines tha...
As part of the BeSSeL Survey, we have used the Very Long Baseline Array to measure 16 trigonometric parallaxes and proper motions of molecular masers associated with 14 high-mass star-forming regions in the Scutum arm in the first quadrant of the Milky Way. This increases the number of maser sources with accurate distances in this arm to 42. The Sc...
Studying the interplay between massive star formation and the interstellar medium (ISM) is paramount to understand the evolution of galaxies. Radio continuum (RC) emission serves as an extinction-free tracer of both massive star formation and the energetic components of the interstellar medium. We present a multi-band radio continuum survey of the...
Class II methanol (CH 3 OH) masers are amongst the clearest signposts of recent high-mass star formation (HMSF). A complete catalogue outlines the distribution of star formation in the Galaxy, the number of young star-forming cores, and the physical conditions of their environment, made possible by the Global View on Star Formation (GLOSTAR) survey...
Class II methanol (CH$_{3}$OH) masers are amongst the clearest signposts of recent high-mass star formation (HMSF). A complete catalogue outlines the distribution of star formation in the Galaxy, the number of young star-forming cores, and the physical conditions of their environment. The Global View on Star Formation (GLOSTAR) survey, which is a b...
We present extensive multi-frequency VLA and VLBA observations of the radio-bright supernova (SN) IIb SN 2004C that span $\sim(40-2793)$ days post-explosion. We interpret the temporal evolution of the radio spectral energy distribution (SED) in the context of synchrotron self-absorbed (SSA) emission from the explosion's forward shock as it expands...
The Cygnus X complex is covered by the Global View of Star Formation in the Milky Way (GLOSTAR) survey, an unbiased radio-wavelength Galactic plane survey, in 4–8 GHz continuum radiation and several spectral lines. The GLOSTAR survey observed the 6.7 GHz transition of methanol (CH 3 OH), an exclusive tracer of high-mass young stellar objects. Using...
Aims. Surveys of the Milky Way at various wavelengths have changed our view of star formation in our Galaxy considerably in recent years. In this paper we give an overview of the GLOSTAR survey, a new survey covering large parts (145 square degrees) of the northern Galactic plane using the Karl G. Jansky Very Large Array in the frequency range 4−8...
Surveys of the Milky Way at various wavelengths have changed our view of star formation in our Galaxy considerably in recent years. In this paper we give an overview of the GLOSTAR survey, a new survey covering large parts (145 square degrees) of the northern Galactic plane using the Karl G. Jansky Very Large Array (JVLA) in the frequency range 4-8...
Context. The Central Molecular Zone (CMZ), a ∼200 pc sized region around the Galactic Centre, is peculiar in that it shows a star formation rate (SFR) that is suppressed with respect to the available dense gas. To study the SFR in the CMZ, young stellar objects (YSOs) can be investigated. Here we present radio observations of 334 2.2 μm infrared so...
The Central Molecular Zone (CMZ), a $\sim$200 pc sized region around the Galactic Centre, is peculiar in that it shows a star formation rate (SFR) that is suppressed with respect to the available dense gas. To study the SFR in the CMZ, young stellar objects (YSOs) can be investigated. Here we present radio observations of 334 2.2 $\mu$m infrared so...
Context. The properties of the population of Galactic supernova remnants (SNRs) are essential to our understanding of the dynamics of the interstellar medium (ISM) in the Milky Way. However, the completeness of the catalog of Galactic SNRs is expected to be only ~30%, with on order 700 SNRs yet to be detected. Deep interferometric radio continuum s...
Context. The properties of the population of the Galactic Supernova Remnants (SNRs) are essential to our understanding of the dynamics of the Milky Way's interstellar medium (ISM). However, the completeness of the catalog of Galactic SNRs is expected to be only ${\sim}30\%$, with on order 700 SNRs yet to be detected. Deep interferometric radio cont...
We have measured trigonometric parallaxes for four H 2 O masers associated with distant massive young stars in the inner regions of the Galaxy using the Very Long Baseline Array as part of the BeSSeL Survey. G026.50 + 0.28 is located at the near end of the Galactic bar, perhaps at the origin of the Norma spiral arm. G020.77−0.05 is in the Galactic...
We have measured trigonometric parallaxes for four water masers associated with distant massive young stars in the inner regions of the Galaxy using the VLBA as part of the BeSSeL Survey. G026.50$+$0.28. is located at the near end of the Galactic bar, perhaps at the origin} of the Norma spiral arm. G020.77$-$0.05 is in the Galactic Center region an...
Context. The derived physical parameters for young H II regions are normally determined assuming the emission region to be optically thin. However, this assumption is unlikely to hold for young H II regions such as hyper-compact H II (HC H II ) and ultra-compact H II (UC H II ) regions and leads to underestimation of their properties. This can be o...
Context. Molecular clouds, which harbor the birthplaces of stars, form out of the atomic phase of the interstellar medium (ISM). To understand this transition process, it is crucial to investigate the spatial and kinematic relationships between atomic and molecular gas.
Aims. We aim to characterize the atomic and molecular phases of the ISM and set...
Context. The Faraday rotation measure (RM) is often used to study the magnetic field strength and orientation within the ionized medium of the Milky Way. Recent observations indicate an RM magnitude in the spiral arms that exceeds the commonly assumed range. This raises the question of how and under what conditions spiral arms create such strong Fa...
Molecular clouds, which harbor the birthplaces of stars, form out of the atomic phase of the interstellar medium (ISM). We aim to characterize the atomic and molecular phases of the ISM and set their physical properties into the context of cloud formation processes. We studied the cold neutral medium (CNM) by means of $\rm HI$ self-absorption (HISA...
We present multiepoch observations with the Very Long Baseline Array of SiO maser emission in the v = 1, J = 1−0 transition at 43 GHz from the remnant of the red nova V838 Mon. We modeled the positions of maser spots to derive a parallax of 0.166 ± 0.060 mas. Combining this parallax with other distance information results in a distance of 5.6 ± 0.5...
We report measurements with the Very Long Baseline Array of the proper motion of Sgr A* relative to two extragalactic radio sources spanning 18 yr. The apparent motion of Sgr A* is −6.411 ± 0.008 mas yr ⁻¹ along the Galactic plane and −0.219 ± 0.007 mas yr ⁻¹ toward the North Galactic Pole. This apparent motion can almost entirely be attributed to...
The continuum emission from 1 to 2 GHz of The H i/OH/Recombination line survey of the inner Milky Way (THOR) at ≲18 arcsec resolution covers ∼132 deg2 of the Galactic plane and detects 10 387 sources. Similarly, the first data release of the Global View of Star Formation in the Milky Way (GLOSTAR) survey covers ∼16 deg2 of the Galactic plane from 4...
Almost all dwarf galaxies in the Local Group (LG) that are not satellites of the Milky Way or M 31 belong to either one of two highly symmetric planes. It is still a matter of debate whether these planar structures are dynamically stable or whether they only represent a transient alignment. Proper motions, if they could be measured, could help to d...
We report measurements with the Very Long Baseline Array of the proper motion of Sgr A* relative to two extragalactic radio sources spanning 18 years. The apparent motion of Sgr A* is -6.411 +/- 0.008 mas/yr along the Galactic plane and -0.219 +/- 0.007 mas/yr toward the North Galactic Pole. This apparent motion can almost entirely be attributed to...
The continuum emission from 1 to 2 GHz of The HI/OH/Recombination line survey of the inner Milky Way (THOR) at $\lesssim$18" resolution covers $\sim 132$ square degrees of the Galactic plane and detects 10387 sources. Similarly, the first data release of the Global View of Star Formation in the Milky Way (GLOSTAR) surveys covers $\sim 16$ square de...
Almost all dwarf galaxies in the Local Group that are not satellites of the Milky Way or M31, belong to either one of two highly-symmetric planes. It is still a matter of debate, whether these planar structures are dynamically stable or whether they only represent a transient alignment. Proper motions, if they could be measured, could help to discr...
We compile and analyze approximately 200 trigonometric parallaxes and proper motions of molecular masers associated with very young high-mass stars. Most of the measurements come from the BeSSeL Survey using the VLBA and the Japanese VERA project. These measurements strongly suggest that the Milky Way is a four-arm spiral, with some extra arm segme...
We compile and analyze ~200 trigonometric parallaxes and proper motions of molecular masers associated with very young high-mass stars. These measurements strongly suggest that the Milky Way is a four-arm spiral. Fitting log-periodic spirals to the locations of the masers, allows us to significantly expand our view of the structure of the Milky Way...
Context . Radio continuum surveys of the Galactic plane are an excellent way to identify different source populations such as planetary nebulae, H II regions, and radio stars and characterize their statistical properties. The Global View of Star Formation in the Milky Way (GLOSTAR) survey will study the star formation in the Galactic plane between...
The GLOSTAR survey will study the star formation in the Galactic plane between $-2^{\circ}< \textit{l}< 85^{\circ}$ and $|b| < 1^{\circ}$ with unprecedented sensitivity in both, flux density ($\sim$ 40 $\mu Jy$ beam$^{-1}$) and range of angular scales ($\sim$ 1."5 to the largest radio structures in the Galaxy). In this paper we present the first re...
As part of the BeSSeL Survey, we report trigonometric parallaxes and proper motions of molecular maser sources associated with 13 distant high-mass star-forming regions in the Sagittarius spiral arm of the Milky Way. In particular, we obtain improved parallax distance estimates for three well-studied regions: 1.9 -0.1+0.1 kpc for M17, - 5.3 -0.9+1....
Context . An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of low luminosity active galactic nuclei (LLAGNs)...
An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc sized accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of Low Luminosity Active Galactic Nuclei (LLAGNs). Th...
As part of the BeSSeL Survey, we report trigonometric parallaxes and proper motions of molecular maser sources associated with 13 distant high mass star forming regions in the Sagittarius spiral arm of the Milky Way. In particular, we obtain improved parallax distance estimates for three well studied regions: 1.9 +0.1/-0.1 kpc for M17, 5.3 +1.3/-0....
We present images of radio recombination lines (RRLs) at wavelengths around 18 cm from the star-forming region W49A to determine the kinematics of ionized gas in the THOR survey (The HI/OH/Recombination line survey of the inner Milky Way) at an angular resolution of 16.8"x13.8". The distribution of ionized gas appears to be affected by feedback pro...
Context Radio continuum surveys of the Galactic plane can find and characterize H II regions, supernova remnants (SNRs), planetary nebulae (PNe), and extragalactic sources. A number of surveys at high angular resolution (≤25 ″ ) at different wavelengths exist to study the interstellar medium (ISM), but no comparable high-resolution and high-sensiti...
Radio continuum surveys of the Galactic plane can find and characterize HII regions, supernova remnants (SNRs), planetary nebulae (PNe), and extragalactic sources. A number of surveys at high angular resolution (<25'') at different wavelengths exist to study the interstellar medium (ISM), but no comparable high-resolution and high-sensitivity surve...
The hydroxyl radical (OH) is present in the diffuse molecular and partially atomic phases of the interstellar medium (ISM), but its abundance relative to hydrogen is not clear. We aim to evaluate the abundance of OH with respect to molecular hydrogen using OH absorption against cm-continuum sources over the first Galactic quadrant. This OH study is...
Context. The hydroxyl radical (OH) is present in the diffuse molecular and partially atomic phases of the interstellar medium (ISM), but its abundance relative to hydrogen is not clear.
Aims. We aim to evaluate the abundance of OH with respect to molecular hydrogen using OH absorption against cm-continuum sources over the first Galactic quadrant.
M...