分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
Y. T. Yan
C. Henkel
K. M. Menten
Y. Gong
H. Nguyen
J. Ott
A. Ginsburg
T. L. Wilson
A. Brunthaler
A. Belloche
J. S. Zhang
N. Budaiev
D.Jeff
摘要： We report the discovery of widespread maser emission in non-metastable inversion transitions of NH_3 toward various parts of the Sagittarius B2 molecular cloud/star forming region complex: We detect masers in the J,K= (6,3), (7,4), (8,5), (9,6), and (10,7) transitions toward Sgr B2(M) and Sgr B2(N), an NH_3 (6,3) maser in Sgr B2(NS), and NH_3 (7,4), (9,6), and (10,7) masers in Sgr B2(S). With the high angular resolution data of the Karl G. Jansky Very Large Array (JVLA) in A-configuration we identify 18 maser spots. Nine maser spots arise from Sgr B2(N), one from Sgr B2(NS), five from Sgr B2(M), and three in Sgr B2(S). Compared to our Effelsberg single dish data, the JVLA data indicate no missing flux. The detected maser spots are not resolved by our JVLA observations. Lower limits to the brightness temperature are >3000~K and reach up to several 10^5~K, manifesting the lines' maser nature. In view of the masers' velocity differences with respect to adjacent hot molecular cores and/or UCH{\scriptsize II} regions, it is argued that all the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCH{\scriptsize II} regions. Overall, Sgr B2 is unique in that it allows us to measure many NH_3 masers simultaneously, which may be essential to elucidate their so far poorly understood origin and excitation.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Y. T. Yan
C. Henkel
C. Kobayashi
K. M. Menten
Y. Gong
J. S. Zhang
H. Z. Yu
K. Yang
J. J. Xie
Y. X. Wang
摘要： With the IRAM 30 meter telescope, we performed observations of the $J$ = 2-1 transitions of CS, C$^{33}$S, C$^{34}$S, C$^{36}$S, $^{13}$CS, $^{13}$C$^{33}$S, and $^{13}$C$^{34}$S as well as the $J$ = 3-2 transitions of C$^{33}$S, C$^{34}$S, C$^{36}$S, and $^{13}$CS toward a large sample of 110 HMSFRs. We measured the $^{12}$C/$^{13}$C, $^{32}$S/$^{34}$S, $^{32}$S/$^{33}$S, $^{32}$S/$^{36}$S, $^{34}$S/$^{33}$S, $^{34}$S/$^{36}$S, and $^{33}$S/$^{36}$S abundance ratios with rare isotopologs of CS, thus avoiding significant saturation effects. With accurate distances obtained from parallax data, we confirm previously identified $^{12}$C/$^{13}$C and $^{32}$S/$^{34}$S gradients as a function of galactocentric distance (RGC). In the CMZ, $^{12}$C/$^{13}$C ratios are higher than suggested by a linear fit to the disk values as a function of RGC. While $^{32}$S/$^{34}$S ratios near the Galactic center and in the inner disk are similar, this is not the case for $^{12}$C/$^{13}$C, when comparing central values with those near RGC of 5 kpc. As was already known, there is no $^{34}$S/$^{33}$S gradient but the average ratio of 4.35~$\pm$~0.44 derived from the $J$ = 2-1 transition lines of C$^{34}$S and C$^{33}$S is well below previously reported values. A comparison between solar and local interstellar $^{32}$S/$^{34}$S and $^{34}$S/$^{33}$S ratios suggests that the Solar System may have been formed from gas with a particularly high $^{34}$S abundance. For the first time, we report positive gradients of $^{32}$S/$^{33}$S, $^{34}$S/$^{36}$S, $^{33}$S/$^{36}$S, and $^{32}{\rm S}/^{36}{\rm S}$ in our Galaxy. The predicted $^{12}$C/$^{13}$C ratios from the latest GCE models are in good agreement with our results. While $^{32}$S/$^{34}$S and $^{32}$S/$^{36}$S ratios show larger differences at larger RGC, $^{32}$S/$^{33}$S ratios show an offset across the entire inner 12 kpc of the Milky Way.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
R. Dokara
Y. Gong
W. Reich
M. Rugel
A. Brunthaler
K. Menten
W. Cotton
S. Dzib
S. Khan
S. Medina
H. Nguyen
G. Ortiz-León
J. Urquhart
F. Wyrowski
A. Yang
L. D. Anderson
H. Beuther
T. Csengeri
P. Müller
J. Ott
摘要： 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 (GLOSTAR) survey, in the Galactic longitude
range $-2^\circ
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational collapse is one of the most important processes in high-mass star formation. Compared with the classic blue-skewed profiles, redshifted absorption against continuum emission is a more reliable method to detect inward motions within high-mass star formation regions. We aim to test if methanol transitions can be used to trace infall motions within high-mass star formation regions. Using the Effelsberg-100 m, IRAM-30 m, and APEX-12 m telescopes, we carried out observations of 37 and 16 methanol transitions towards two well-known collapsing dense clumps, W31C (G10.6-0.4) and W3(OH), to search for redshifted absorption features or inverse P-Cygni profiles. Redshifted absorption is observed in 14 and 11 methanol transitions towards W31C and W3(OH), respectively. The infall velocities fitted from a simple two-layer model agree with previously reported values derived from other tracers, suggesting that redshifted methanol absorption is a reliable tracer of infall motions within high-mass star formation regions. Our observations indicate the presence of large-scale inward motions, and the mass infall rates are roughly estimated to be $\gtrsim$10$^{-3}$ $M_{\odot}$yr$^{-1}$, which supports the global hierarchical collapse and clump-fed scenario. With the aid of bright continuum sources and the overcooling of methanol transitions leading to enhanced absorption, redshifted methanol absorption can trace infall motions within high-mass star formation regions hosting bright H{\scriptsize II} regions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Zs. M. Szabó
Y. Gong
K. M. Menten
W. Yang
C. J. Cyganowski
Á. Kóspál
P. Ábrahám
A. Belloche
F. Wyrowski
摘要： FU Orionis (FUor) and EX Lupi (EXor) type objects represent two small, but rather spectacular groups of low-mass, young eruptive stars. Outbursts of several magnitudes are observed, attributed to enhanced accretion from the circumstellar disk onto the central protostar. The host molecular environments of FUors/EXors are poorly explored due to the scarcity of systematic molecular line observations. We carried out the first dedicated survey of the molecular environments of a large sample of FUors/EXors, observing a total of 51 sources with the aim of studying the ammonia (NH$_3$) emission in their host environments. We observed the ammonia (J,K)=(1,1), (2,2), and (3,3) inversion transitions using the Effelsberg 100-m radio telescope. We derived H$_2$ column densities and dust temperatures using archival Herschel SPIRE data. We detected the (1,1) transition toward 28 sources and the (2,2) transition toward 12 sources, while the (3,3) transition was detected toward only two sources. We find kinetic temperatures between ~12 K and 21 K, ammonia column densities from $5.2\times10^{13}\,cm^{-2}$ to $3.2\times10^{15}\,cm^{-2}$, and fractional ammonia abundances with respect to H$_{2}$ from $4.7\times10^{-9}$ to $1.5\times10^{-7}$. The results are comparable to those found in infrared dark clouds (IRDCs). Kinetic analysis suggests that most of the eruptive stars in our sample reside in rather quiescent (sonic or transonic) host environments. Our NH$_3$ observations and analysis of the SPIRE dust-based H$_2$ column density maps confirm the presence of dense material toward 7 sources in our sample; additional sources might also harbour dense gas based on their NH$_2$ (2,2) detections, might indicate an earlier phase than originally classified. Based on our results, we suggest observations targeting additional molecular lines would help to refine the evolutionary classification of eruptive stars.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
S. A. Dzib
A. Y. Yang
J. S. Urquhart
S. -N. X. Medina
A. Brunthaler
K. M. Menten
F. Wyrowski
W. D. Cotton
R. Dokara
G. N. Ortiz-León
M. R. Rugel
H. Nguyen
Y. Gong
A. Chakraborty
H. Beuther
S. J. Billington
C. Carrasco-Gonzalez
T. Csengeri
P. Hofner
J. Ott
摘要： 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 that are sensitive to emission on angular scales $<4"$. The resulting radio continuum images have an angular resolution of 1.0", and sensitivity of $\sim60 \mu$Jy~beam$^{-1}$; making it the most sensitive radio survey covering a large area of the Galactic plane with this angular resolution. An automatic source extraction algorithm was used in combination with visual inspection to identify a total of 3325 radio sources. A total of 1457 radio sources are $\geq7\sigma$ and comprise our highly reliable catalog; 72 of these are grouped as 22 fragmented sources, e.g., multiple components of an extended and resolved source. To explore the nature of the catalogued radio sources we searched for counterparts at millimeter and infrared wavelengths. Our classification attempts resulted in 93 HII region candidates, 104 radio stars, 64 planetary nebulae, while most of the remaining radio sources are suggested to be extragalactic sources. We investigated the spectral indices ($\alpha$, $S_\nu\propto\nu^\alpha$) of radio sources classified as HII region candidates and found that many have negative values. This may imply that these radio sources represent young stellar objects that are members of the star clusters around the high mass stars that excite the HII regions, but not these HII regions themselves. By comparing the peak flux densities from the GLOSTAR and CORNISH surveys we have identified 49 variable radio sources, most of them with an unknown nature. Additionally, we provide the list of 1866 radio sources detected within 5 to 7$\sigma$ levels.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Y. T. Yan
C. Henkel
K. M. Menten
Y. Gong
H. Nguyen
J. Ott
A. Ginsburg
T. L. Wilson
A. Brunthaler
A. Belloche
J. S. Zhang
N. Budaiev
D. Jeff
摘要： We report the discovery of widespread maser emission in non-metastable inversion transitions of NH$_3$ toward various parts of the Sagittarius B2 molecular cloud/star forming region complex: We detect masers in the $J,K = $ (6,3), (7,4), (8,5), (9,6), and (10,7) transitions toward Sgr B2(M) and Sgr B2(N), an NH$_3$ (6,3) maser in Sgr B2(NS), and NH$_3$ (7,4), (9,6), and (10,7) masers in Sgr B2(S). With the high angular resolution data of the Karl G. Jansky Very Large Array (JVLA) in A-configuration we identify 18 maser spots. Nine maser spots arise from Sgr B2(N), one from Sgr B2(NS), five from Sgr B2(M), and three in Sgr B2(S). Compared to our Effelsberg single dish data, the JVLA data indicate no missing flux. The detected maser spots are not resolved by our JVLA observations. Lower limits to the brightness temperature are $>$3000~K and reach up to several 10$^5$~K, manifesting the lines' maser nature. In view of the masers' velocity differences with respect to adjacent hot molecular cores and/or UCH{\scriptsize II} regions, it is argued that all the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCH{\scriptsize II} regions. Overall, Sgr B2 is unique in that it allows us to measure many NH$_3$ masers simultaneously, which may be essential to elucidate their so far poorly understood origin and excitation.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
C. Gong
X. Yang
S. J. Tang
Q. Q. Zhang
Y. Wang
Y. L. Liu
Y. C. Chen
G. D. Peng
X. Fan
Y. F. Xiao
Y. J. Rao
Y. Gong
摘要： Biomarker detection is the key to identifying health risks. However, designing sensitive biosensors in a single-use mode for disease diagnosis remains a major challenge. Here, we report sub-monolayer biolasers with remarkable repeatability for ultrasensitive and disposable biomarker detection. The biolaser sensors are designed by employing the telecom optical fibers as distributed optical microcavities and pushing the gain molecules down to the sub-monolayer level. We observe a status transition from the monolayer biolaser to the sub-monolayer biolaser by tuning the specific conjugation. By reducing the fluorophores down to the threshold density (~ 3.2 x 10-13 mol/cm2), we demonstrate an ultimate sensitivity of sub-monolayer biolaser with six orders of magnitude enhancement compared with the monolayer biolasers. We further achieved ultrasensitive immunoassay for Parkinson's disease biomarker, alpha-synuclein, with a lower limit of detection of 0.32 pM in serum. This biosensor with massive fabrication capability at ultralow cost provides a general method for the ultrasensitive disposable biodetection of disease biomarkers.
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