اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدEvidence for CO shock excitation in NGC 6240 from Herschel SPIRE spectroscopy
114
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines are detected, including CO J=4-3 through J=13-12, 6 H2O rotational lines, and [CI] and [NII] fine-structure lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the CO ladders of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the excitation of the gas in NGC 6240. We applied both C and J shock models to the H2 v=1-0 S(1) and v=2-1 S(1) lines and the CO rotational ladder. The CO ladder is best reproduced by a model with shock velocity v_s=10 km s^-1 and a pre-shock density n_H=5 * 10^4 cm^-3. We find that the solution best fitting the H2 lines is degenerate: The shock velocities and number densities range between v_s = 17 - 47 km s^-1 and n_H=10^7 - 5 * 10^4 cm^-3, respectively. The H2 lines thus need a much more powerful shock than the CO lines. We deduce that most of the gas is currently moderately stirred up by slow (10 km s^-1) shocks while only a small fraction (< 1 percent) of the ISM is exposed to the high velocity shocks. This implies that the gas is rapidly loosing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.
قيم البحث
اقرأ أيضاً
We present full spectral scans from 200-670$mu$m of 26 Class 0+I protostellar sources, obtained with $Herschel$-SPIRE, as part of the COPS-SPIRE Open Time program, complementary to the DIGIT and WISH Key programs. Based on our nearly continuous, line
-free spectra from 200-670 $mu$m, the calculated bolometric luminosities ($L_{rm bol}$) increase by 50% on average, and the bolometric temperatures ($T_{rm bol}$) decrease by 10% on average, in comparison with the measurements without Herschel. Fifteen protostars have the same Class using $T_{rm bol}$ and $L_{rm bol}$/$L_{rm submm}$. We identify rotational transitions of CO lines from J=4-3 to J=13-12, along with emission lines of $^{13}$CO, HCO$^+$, H$_{2}$O, and [CI]. The ratios of $^{12}$CO to $^{13}$CO indicate that $^{12}$CO emission remains optically thick for $J_{rm up}$ < 13. We fit up to four components of temperature from the rotational diagram with flexible break points to separate the components. The distribution of rotational temperatures shows a primary population around 100 K with a secondary population at $sim$350 K. We quantify the correlations of each line pair found in our dataset, and find the strength of correlation of CO lines decreases as the difference between $J$-level between two CO lines increases. The multiple origins of CO emission previously revealed by velocity-resolved profiles are consistent with this smooth distribution if each physical component contributes to a wide range of CO lines with significant overlap in the CO ladder. We investigate the spatial extent of CO emission and find that the morphology is more centrally peaked and less bipolar at high-$J$ lines. We find the CO emission observed with SPIRE related to outflows, which consists two components, the entrained gas and shocked gas, as revealed by our rotational diagram analysis as well as the studies with velocity-resolved CO emission.
We analyse Herschel/SPIRE images of the edge-on spiral galaxy NGC 891 at 250, 350 and 500 micron. Using a 3D radiative transfer model we confirm that the dust has a radial fall-off similar to the stellar disk. The dust disk shows a break at about 12
kpc from the center, where the profile becomes steeper. Beyond this break, emission can be traced up to 90% of the optical disk in the NE side. On the SW, we confirm dust emission associated with the extended, asymmetric HI disk, previously detected by the Infrared Space Observatory (ISO). This emission is marginally consistent with the large diffuse dust disk inferred from radiative transfer fits to optical images. No excess emission is found above the plane beyond that of the thin, unresolved, disk.
We present the first Herschel spectroscopic detections of the [OI]63 and [CII]158 micron fine-structure transitions, and a single para-H2O line from the 35 x 15 kpc^2 shocked intergalactic filament in Stephans Quintet. The filament is believed to hav
e been formed when a high-speed intruder to the group collided with clumpy intergroup gas. Observations with the PACS spectrometer provide evidence for broad (> 1000 km s^-1) luminous [CII] line profiles, as well as fainter [OI]63micron emission. SPIRE FTS observations reveal water emission from the p-H2O (111-000) transition at several positions in the filament, but no other molecular lines. The H2O line is narrow, and may be associated with denser intermediate-velocity gas experiencing the strongest shock-heating. The [CII]/PAH{tot) and [CII]/FIR ratios are too large to be explained by normal photo-electric heating in PDRs. HII region excitation or X-ray/Cosmic Ray heating can also be ruled out. The observations lead to the conclusion that a large fraction the molecular gas is diffuse and warm. We propose that the [CII], [OI] and warm H2 line emission is powered by a turbulent cascade in which kinetic energy from the galaxy collision with the IGM is dissipated to small scales and low-velocities, via shocks and turbulent eddies. Low-velocity magnetic shocks can help explain both the [CII]/[OI] ratio, and the relatively high [CII]/H2 ratios observed. The discovery that [CII] emission can be enhanced, in large-scale turbulent regions in collisional environments has implications for the interpretation of [CII] emission in high-z galaxies.
We present the observations of the starburst galaxy M82 taken with the Herschel SPIRE Fourier Transform Spectrometer. The spectrum (194-671 {mu}m) shows a prominent CO rotational ladder from J = 4-3 to 13-12 emitted by the central region of M82. The
fundamental properties of the gas are well constrained by the high J lines observed for the first time. Radiative transfer modeling of these high-S/N 12CO and 13CO lines strongly indicates a very warm molecular gas component at ~500 K and pressure of ~3x10^6 K cm^-3, in good agreement with the H_2 rotational lines measurements from Spitzer and ISO. We suggest that this warm gas is heated by dissipation of turbulence in the interstellar medium (ISM) rather than X-rays or UV flux from the straburst. This paper illustrates the promise of the SPIRE FTS for the study of the ISM of nearby galaxies.
We describe the generation of single-band point source catalogues from submillimetre Herschel-SPIRE observations taken as part of the Science Demonstration Phase of the Herschel Multi-tiered Extragalactic Survey (HerMES). Flux densities are found by
means of peak-finding and the fitting of a Gaussian point-response function. With highly-confused images, careful checks must be made on the completeness and flux density accuracy of the detected sources. This is done by injecting artificial sources into the images and analysing the resulting catalogues. Measured flux densities at which 50 per cent of injected sources result in good detections at (250, 350, 500) {mu}m range from (11.6, 13.2, 13.1) mJy to (25.7, 27.1, 35.8) mJy, depending on the depth of the observation (where a `good detection is taken to be one with positional offset less than one full-width half-maximum of the point-response function, and with the measured flux density within a factor of 2 of the flux density of the injected source). This paper acts as a reference for the 2010 July HerMES public data release.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
