Blue Lobe Research Articles

Hubble Space TelescopeSpace Telescope Imaging Spectrograph Observations of the Bipolar Jet from RW Aurigae: Tracing Outflow Asymmetries Close to the Source

We have observed the bipolar jet from RW Aur A with STIS on board the Hubble Space Telescope. After continuum subtraction, morphological and kinematic properties of this outflow can be traced to within 01 from the source in forbidden emission lines. The jet appears well collimated, with typical FWHMs of 20-30 AU in the first 2'' and, surprisingly, does not show a separate low-velocity component, in contrast to earlier observations. The systemic radial outflow velocity of the blueshifted lobe is typically 50% larger than that of the redshifted one with a velocity difference of about 65 km s-1. Although such asymmetries have been seen before on larger scales, our high spatial resolution observations suggest that they are intrinsic to the central engine rather than effects of the star's immediate environment. Temporal variations of the bipolar jet's outflow velocities appear to occur on timescales of a few years. They have combined to produce a 55% increase in the velocity asymmetry between the two lobes over the past decade. In the red lobe, estimated mass flux (j) and momentum flux (j) values are around one-half and one-third of those for the blue lobe, respectively. The mass outflow to mass accretion rate is 0.05, the former being measured at a distance of 035 from the source.

Spectropolarimetry in a sunspot penumbra

Stokes profiles of sunspot penumbrae show distinct asymmetries, which point to gradients in the velocity field and in the magnetic field. We present spectropolarimetric measurements of the Stokes vector in the neutral iron triplet at 1564.8 nm taken with the Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope (VTT) in Tenerife. We report on the peculiarities of the profiles of circularly and linearly polarized light for spots at different heliocentric angles. We elaborate on the spatial dependence of Stokes asymmetries within the penumbra and find for profiles of circularly polarized light: (1) In the center-side penumbra the amplitude difference of Stokes-V exhibits a sign reversal on a radial cut, i.e., in the inner (outer) penumbra the red (blue) lobe is broader and shows a smaller amplitude than the blue (red) lobe. (2) In the outer limb-side penumbra (beyond the magnetic neutral line) the red lobe is broader and of less amplitude than the blue lobe. (3) Along the magnetic neutral line we find abnormal Stokes-V profiles, which consist of more than 2 lobes. This indicates the presence of two polarities. For small heliocentric angles abnormal profiles are also seen beyond the magnetic neutral line in the outer penumbra. (4) Maps of the net circular polarization have the tendency to be antisymmetric with respect to the axis that connects disk center with spot center. This finding is striking, because corresponding maps for Fe I 630.25 are symmetric. For linearly polarized profiles we extract the following features: (5) On the center-side penumbra at a heliocentric angle of 56° a Doppler-shift as high as 5 km s-1 can be directly measured by the splitting of the π-component of the linearly polarized component. (6) In limb-side penumbrae, the profiles of the π-component show the typical asymmetry properties of the Evershed flow as observed in Stokes-I of magnetically insensitive lines. (7) In the outer center- and limb-side penumbrae the center of the π-component is blue-shifted relative to the zero-crossing of the V-profile. Motivated by the moving tube model of Schlichenmaier et al. ([CITE]), we construct simple model atmospheres featuring hot upflows and cool outflows and calculate corresponding synthetic V-profiles. These profiles are compared with our measured ones and with observed V-profiles in Fe I 630.25 from other authors. We find that the synthetic V-profiles can reproduce all essential characteristics of observed V-profiles for both lines.

Disks and outflows around intermediate-mass stars and protostars

In order to study the existence and evolution of circumstellar disks around intermediate-mass stars (M 3M), we have obtained single-dish and interferometric continuum images at 2.6 mm and 1.3 mm of the intermediate-mass protostar NGC 7129 FIRS 2 and of the Herbig Be stars LkH 234 and HD 200775. These objects are representative of the dierent stages of the pre-main sequence evolution with ages ranging from a few 10 3 to 8 10 6 years. Single-dish and interferometric observations of the outflows associated with these sources are also presented. In NGC 7129 FIRS 2, two millimeter sources are required to t the interferometric 1.3 mm continuum emission. Only the most intense of these millimeter objects, FIRS 2 { MM1, seems to be associated with the CO outflow. The second and weaker source, FIRS 2 { MM2, does not present any sign of stellar activity. The single-dish map of the CO outflow presents an unusual morphology with the blue and red lobes separated by an angle of 82 .T he COJ =1 ! 0 interferometric image shows that this unusual morphology is the result of the superposition of two outflows, one of them associated with FIRS 2 { MM1 (the blue lobe in the single-dish map) and the other (the red lobe) with a new infrared source (FIRS 2 { IR) which is not detected in the millimeter continuum images. The interferometric 1.3 mm continuum image of NGC 7129 FIRS 1 reveals that LkH 234 is a member of a cluster of embedded objects. Two millimeter clumps are detected in this far-infrared source. The strongest is spatially coincident with the mid-infrared companion of LkH 234, IRS 6. A new millimeter clump, FIRS 1 { MM1, is detected at an oset ( 3:23 00 ,3 .0 00 )f rom LkH 234. We have not detected any compact source towards LkH 234 with a limit for the mass of a circumstellar disk, MD < 0.1 M. The comparison of the interferometric CO J =1 ! 0 and continuum images reveals that IRS 6 very likely drives the energetic molecular outflow detected towards NGC 7129 FIRS 1 and the (SII) jet. The extremely young object FIRS 1 { MM1 (it has not been detected in the near-and mid-infrared) turns out to be the driving source of the H2 jet. There is no evidence for the existence of a bipolar outflow associated with LkH 234. We have not detected 1.3 mm continuum emission towards HD 200775. Our observations imply a 3- upper limit of < 0.002 M for the mass of a circumstellar disk. This is the lowest upper limit obtained so far in a Herbig Be star. Thus our observations provide new important information on three protostars (IRS 6, FIRS 1 { MM1 and FIRS 2 { MM1), one infrared star (FIRS 2 { IR) and two Herbig Be stars. The luminosities of the protostars are consistent with being intermediate-mass objects (M 3:5{4:5 M). They are surrounded by thick envelopes with masses ranging between2 3:5 M and drive energetic outflows. Circumstellar disks and bipolar outflows are not detected toward the Herbig Be stars. We have obtained an upper limit for the disk/stellar mass ratio, MD=M ,o f< 0.02 in LkH 234 and of < 0.0002 in HD 200775. Our limit in HD 200775 implies that in evolved Herbig Be stars the MD=M ratio is more than two orders of magnitude lower than in T Tauri and Herbig Ae stars. We propose that in massive stars (M 5 M )b oth the dispersal of the outer disk and the energetic mass-loss, occur early in the stellar evolution before the star becomes visible. Some mechanisms for the dispersal of the outer disk are discussed.

SiO Emission in the Multilobe Outflow Associated with IRAS 16293−2422

We have mapped the thermal emission line of SiO (v = 0; J = 2-1) associated with the quadrupolar molecular outflow driven by the very cold far-infrared source IRAS 16293-2422. The SiO emission is significantly enhanced in the northeastern red lobe and at the position ~50'' east of the IRAS source. Strong SiO emission observed at ~50'' east of the IRAS source presents evidence for a dynamical interaction between a part of the eastern blue lobe and the dense ambient gas condensation; however, such an interaction is unlikely to be responsible for producing the quadrupolar morphology. The SiO emission in the northeastern red lobe shows spatial and velocity structure similar to those of the CO outflow, suggesting that the SiO emission comes from the molecular outflow in the northeastern red lobe itself. The observed velocity structure is reproduced by a simple spatiokinematic model of bow shock with a shock velocity of 19-24 km s-1 inclined by 30°-45° from the plane of the sky. This implies that the northeastern red lobe is independent of the eastern blue lobe and that the quadrupolar structure is due to two separate bipolar outflows. The SiO emission observed in the western red lobe has a broad pedestal shape with low intensity. Unlike the SiO emission in the northeastern red lobe, the spatial extent of the SiO emission in the western red lobe is restricted to its central region. The spatial and velocity structures and the line profiles suggest that three different types of SiO emission are observed in this outflow: the SiO emission arising from the interface between the outflowing gas and the dense ambient gas clump, the SiO emission coming from the outflow lobe itself, and the broad SiO emission with low intensity observed at the central region of the outflow lobe.

Excitation Analysis of SO and SO2in the Proto–Planetary Nebula OH 231.8+4.2

In the nebula OH 231.8+4.2 we have observed SO and SO2 millimeter-wave emission lines having a wide range of excitation energy. The extent of the SO emission was also mapped. Rotation diagrams were derived from these observations, and we deduced the rotation temperatures and relative abundances of SO and SO2 for three different velocity ranges corresponding to the spherical mass-loss envelope and the blue and red lobes of the bipolar outflow. The rotation temperatures for SO and SO2 are higher in the expanding envelope than in the outflow lobes. Subject to modeling uncertainties, the relative abundances of both molecules in the lobes are slightly enhanced by factors 2-5 times relative to the values in the envelope.

A Multitransition HCO+Study in NGC 2264G: Anomalous Emission of theJ = 1 → 0 Line

We present multitransition observations of the HCO+ molecule toward the very young star-forming region associated with the NGC 2264G molecular outflow. Anomalous emission is observed in the lowest rotational transition; the J = 4 → 3 and J = 3 → 2 transitions clearly trace the dense core encompassing the exciting source of the molecular outflow, whereas the HCO+ J = 1 → 0 is barely detected at a much lower intensity and has a much broader line shape. Analysis of the data strongly suggests that the HCO+ J = 1 → 0 emission arising from the core is being absorbed efficiently by a cold low-density envelope around the core or a foreground cloud. This result seems exceptional, yet the J = 1 → 0 HCO+ and HCN emission from other dense cores (especially those in giant molecular clouds) may be affected. In these cases, the rare isotopes of these molecules and higher rotational transitions of the main isotopes should be used to study these regions. Two quiescent clumps, JMG 99 G1 and G2, are detected in the blue lobe of the NGC 2264G molecular outflow, close to shock-excited near-IR H2 knots. These clumps belong to the class of radiatively excited clumps, i.e., the radiation from the shock evaporates the dust mantles and initiates a photochemical process, enhancing the emission of the HCO+.

An Alignment Effect in FR I Radio Galaxies:U‐Band Polarimetry of the Abell 2597 Cluster Central Galaxy

We have obtained U-band polarimetry of the spatially extended optical continuum associated with the FR I radio source PKS 2322-122, located in the Abell 2597 cluster central galaxy. We find a 3 σ upper limit to the degree of optical continuum polarization of less than 6%. The accuracy of the measurement is limited primarily by our ability to measure the amount of diluting galactic starlight. This limit is inconsistent with the continuum being primarily scattered light or synchrotron radiation. We can therefore exclude models that attribute the continuum to scattered light from an active nucleus that is hidden from direct view. Our result does not support the unification paradigm for BL Lac objects and FR I radio sources. Essentially all of the data pertaining to the continuum along the radio source—the blue lobes—indicate that they are regions of recent star formation. The spatial coincidence between the lobes and disturbances in the radio source suggests that star formation may have been induced by an interaction between the radio source and the cool (less than 104 K) surrounding gas. This result, in addition to the results of a similar study of the A1795 cluster central galaxy, shows that under the appropriate conditions FR I radio sources may be capable of inducing significant episodes of star formation in elliptical galaxies. We compare the rest-frame U-band polarized luminosities and 1.4 GHz radio powers of A2597 and A1795 to those for several high-redshift radio galaxies exhibiting the alignment effect. We find that if the polarized luminosities of radio galaxies scale in proportion to their radio luminosities, we would not have detected a polarized signal in either A2597 or A1795. We suggest that the strength of the active galactic nucleus is the fundamental property distinguishing some powerful high-redshift radio galaxies exhibiting the alignment effect from the lower power FR I radio galaxies in cooling flows that exhibit the lobe phenomenon. While both FR I and FR II radio sources seem to be capable of triggering star formation, FR I radio sources seem to be incapable of producing a large enough polarized luminosity to contribute significantly to the aligned continuum radiation.

The Kinematic Properties of HH 311

We present scanning Fabry-Perot observations of HH 311 covering the red [S II] lines. A study of the kinematics of this region shows a number of knots, which appear to be kinematically associated with the HH 111 outflow. We also detect diffuse emission, which appears to be light from the knots that is scattered on dust present in the surrounding environment. A comparison of the line widths of the knots with previously measured proper motions leads us to conclude that HH 311 is moving into a mostly stationary environment. From this, we conclude that it is likely that HH 311 is the leading working surface of the blue lobe of the HH 111 outflow and that no further knots will be discovered at larger distances from the outflow source.

The Powering Source and Origin of the Quadrupolar Molecular Outflow in L723

We present the results of single-dish observations of CS J = 2-1 and J = 3-2 and interferometric observations of CO J = 1-0 toward the center of the quadrupolar molecular outflow in L723. We have detected a compact CS condensation having a size of 0.04 pc and a mass of 0.55 M? toward the northeastern radio continuum source VLA 2 (AER91 2). The CO outflow also shows the distribution centered at VLA 2. These results suggest that the source VLA 2 is the young stellar object that is powering the conspicuous molecular outflow system. On the other hand, there is no enhancement in the CS intensity or the CO outflow distribution toward the southwestern radio continuum source VLA 1 (AER91 1), indicating that the source VLA 1 does not contribute to the morphology of the quadrupolar outflow in L723. The CO distribution observed with the interferometer delineates the western edge of the blue lobe and the northeastern edge of the red lobe revealed in the single-dish map, suggesting that the outflow in L723 is a single bipolar outflow with a wide opening angle of 120?-170? rather than two independent outflows. We found signs of interaction between the blueshifted outflow and the dense ambient gas: (1) there is a compact CS clump blueshifted by ~1 km s-1, the distribution of which shows anticorrelation with the blueshifted CO outflow; (2) both CS and NH3 spectra show the line broadening toward the blueshifted clump; and (3) there is a temperature enhancement at the boundary of the blueshifted clump of CS emission. It is likely that such interaction with the dense ambient gas has the increased opening angle of the outflow, which accounts for the quadrupolar morphology.

Herbig-Haro Flows from the L1641-N Embedded Infrared Cluster

We have discovered a large number of Herbig-Haro (HH) flows associated with the embedded infrared cluster surrounding the IRAS source 05338-0624, the driving source of the L1641-N molecular outflow. The best collimated HH flow in the region, HH 303, stretches in two groups of knots along a well-defined axis from the VLA source that coincides with the IRAS source. This HH flow is coaxial with the blue northern lobe of the molecular flow. To the north-northwest of the cluster we find a long series of very large and finely shaped bow shocks, which stretch on a well-defined axis away from the cluster. The most distant HH object, HH 310, is 6.3 pc in projection from the center of the cluster, making it the largest HH lobe known from a low-mass star. We identify the counterlobe with an already known chain of infrared H2 emission knots. Additionally, we find two very large fragmented bow shocks, HH 403 and 404, to the northeast of and facing away from the cluster. They lie on an axis that passes through the cluster at projected distances of 4.2 and 5.4 pc. In the opposite direction, to the southwest we identify the previously known object HH 127 at a projected distance of 5.2 pc from the cluster and within an angle of 10° of the HH 403/404 axis. HH 127 consists of three faint knots also on a line through the cluster. Precisely south of the VLA source and on the axis of the HH 303 jet, we find a large bow shock, HH 61, which is 5.9 pc in projection from the cluster, and which we believe is part of the counterflow to the HH 303 jet. Our CCD images and 13CO maps clearly show that HH 61 and HH 127 are located just beyond the well-defined edge of the L1641 cloud, which explains why they are optically visible. Our extensive C18O map of the region shows that the cluster is associated with a prominent cloud core. Our 12CO map reveals, in addition to the known L1641-N outflow, a large pair of compact low-velocity outflow lobes, a southeastern blueshifted lobe, and a northwestern redshifted lobe, separated by 2.7 pc and centered on the infrared cluster. The numerous outflows in the region provide evidence that a large number of the young stars in the loose cluster are presently in active mass-losing phases. The L1641-N cluster is clearly the presently most active site of low-mass star formation in the L1641 molecular cloud.

Velocity Shifts in L1228: The Disruption of a Core by an Outflow

We present 12CO(1-0),13CO(1-0), CS(2-1), and C3H2(212-101) observations of the L1228 outflow and dense core with resolutions between 50'' and 25''. The bipolar molecular outflow originates from IRAS 20582+7724 and extends over almost 15' (≈ 1.2 pc). It has a well-collimated blue lobe and a less collimated red lobe, which is split into two branches that diverge from the IRAS position. The two CO outflow lobes are well aligned with previously observed high-excitation emission from H2 and Hα, although these emissions present bendings from a straight line, suggesting that the outflow driving wind changes direction by interacting with the ambient cloud. The dense gas in the core also shows evidence for acceleration in the outflow direction, although its velocity is significantly lower than that of the CO emission. The dense gas acceleration appears in the CS and C3H2 spectra as velocity shifts in the line centroid on the order of one C3H2 full line width (≈ 0.4 km s-1). These shifted line profiles are not accompanied by any significant emission at ambient core velocities. Furthermore, there is very little or no quiescent C3H2 emission toward the outflow lobes, as if the outflow acceleration had been so efficient that all the dense gas has been set into motion. This acceleration, in addition, has occurred without appreciable line width enhancement, suggesting that it has not increased substantially the turbulence of the gas. From the large size of the velocity shifts (comparable to the gas escape velocity) and from our energetics estimates, we infer that the L1228 outflow could significantly disperse the dense gas in the core by the time the outflow phase ends.

Molecular Outflows from X-Ray–Emitting Protostars in the ρ Ophiuchi Dark Cloud

We report CO (J = 2-1, J = 1-0) outflows from four X-ray-emitting protostars (EL29, IRS44, WL6, WL10) in the ρ Ophiuchi cloud core which have been firmly identified with the X-ray satellite ASCA. The common feature of these outflows is that the blue and red lobes are largely overlapped, which indicates that the inclination angle between the outflow axis and line of sight is smaller than 30° (nearly pole-on configuration). Taking account of the hard X-ray transparency (NH ~ 1023 cm-2) and the column density of a circumstellar disk (NH > 1024 cm-2), it is naturally understood that hard X-rays emitted near the surface of protostars or the inner part of the disk are observed in the nearly pole-on configuration. The outflow detection rate (4/5) in the present observations shows that a low-mass protostar emits X-rays even in the outflow phase of early stellar evolution.

Shock Chemistry in the Young Bipolar Outflow L1157

We present the first results from a recent survey of molecular lines in L1157, a highly collimated bipolar molecular outflow driven by a class 0 protostar. These observations are used to study the chemical alterations produced by a violent, highly collimated outflow. Different molecular lines are observed to trace different components of the gas. Some molecules (C3H2, N2H+, H13CO+, DCO+) are abundant in the quiescent medium but are not observed at high velocities. Lines from these molecules are the best tracers of the concentration of dense gas around the protostar. In addition, we find that some otherwise rare molecules (e.g., SiO, CH3OH, H2CO, HCN, CN, SO, and SO2) are enhanced by at least an order of magnitude at the shocked region. Our observations provide estimates of the enhancement factors for such species. Strong gradients in the chemical composition are observed along the outflow blue lobe, which could be due to the evolution in time of the chemical processes. We briefly discuss the chemistry of the most important molecules, devoting special attention to the species that are thought to be abundant in interstellar ice mantles.

The Small‐Scale Structure of the CO Outflow in Barnard 1

We present aperture synthesis CO (J = 1-0) observations of the compact molecular outflow in the dark cloud B1 (Barnard 1). We have detected strong blueshifted emission having a peak brightness temperature of 14.3 K, while no significant emission was detected in the redshifted velocity range. The most prominent feature in our map is a distinct ringlike structure having a size of 25'' (8700 AU) × 14'' (5000 AU) at velocities blueshifted by 1.9-2.7 km s-1 from the systemic velocity. The central hole of the CO ring coincides well with the IRAS position, suggesting that this outflow is driven by the IRAS source, 03301+3057. The CO ring structure is interpreted as a conical outflow lobe with a brightened limb observed from its polar direction. The high-velocity gas that is blueshifted more than 4 km s-1 shows a V-shaped structure open to the southwest. This structure well delineates the northeast edge of the CO blue lobe observed with the single dish, where the CO lobe faces to the dense gas traced by the C18O emission. The strong peak of SiO emission observed by Yamamoto et al. is located at the interface between the CO outflow and the dense gas traced by the C18O and H13CO+ emission. This suggests that the outflow which emanates from the young star strongly interacts with the dense material and causes a shock that propagates into the surrounding cloud. The presence of strong SiO emission and the cold IRAS spectrum (log [Fν(60 μm)/Fν(100 μm)] < -0.76) suggest that the central source of B1 is a candidate for a protostar in the earliest evolutionary stage having an outflow in a nearly pole-on configuration.

Shock Chemistry in Bipolar Molecular Outflows

Chemical studies have a great potential to study the structure and evolution of the bipolar molecular outflows driven by young stellar objects. In this paper, we discuss some very recent mm-wave studies of L 1157, a bipolar molecular outflow driven by a Class 0 protostar. These observations are very useful to illustrate the chemical alterations produced by a violent highly-collimated outflow. Different molecular lines are observed to trace different components of the gas. Some molecules are abundant in the quiescent medium but are not observed in the shock (e.g. C3H2, N2H+, H13CO+, DCO+), whereas some otherwise rare molecules are very enhanced at the shocked region (e.g. SiO, CH3OH, H2CO, HCN, CN, SO, SO2). In addition, we have observed strong gradients in the chemical composition across the outflow blue lobe. We briefly discuss the chemistry of the most important molecules, devoting special attention to the species which are thought to be abundant in interstellar ice mantles.

Three Millimeter Molecular Line Observations of Sagittarius B2. II. High-Resolution Studies of C 18O, HNCO, NH 2CHO, and HCOOCH 3

High-resolution imaging of C<SUP>18</SUP>O, HNCO, NR<SUB>2</SUB>CHO, and RCOOCH<SUB>3</SUB> in Sgr B2 are presented in this study. The C<SUP>18</SUP>O emission comes mainly from the Sgr B2(M) and Sgr B2(N) dense cores and the western gas clump RNO(M). Toward Sgr B2(M), the C<SUP>18</SUP>O column density is 2 times higher and the fractional abundance is 80 times higher than toward Sgr B2(N). In HNO(M), the narrow line width implies that the C<SUP>18</SUP>O emission arises from the diffuse gas. The complex molecules NR<SUB>2</SUB>CHO and HCOOCR<SUB>3</SUB> were detected only toward the Sgr B2(N) core. The HNCO K<SUB>-1</SUB> = 2 emission is detected only in Sgr B2(N) and is attributed to efficient radiative pumping, which indicates the significant presence of far-infrared field and warm dust grains. Only 4% of the HNCO was found in the K<SUB>-1</SUB> = 0 ladders in Sgr B2(N). The nondetection of the K<SUB>-1</SUB> = 2 emission toward Sgr B2(M) is caused by excitation and low abundance. In contrast, the HNCO K<SUB>-1</SUB> = 0 emission comes mainly from the extended gas component: the far northern region and HNCO(SW). For the K<SUB>-1</SUB> = 0 transitions, T<SUB>rot</SUB> = ∼7 K. The low T<SUB>rot</SUB> and the apparent ubiquity of RNCO suggest that abundant HNCO exists in the Sgr B2 envelope. The HNCO K<SUB>-1</SUB> = 0 emission unveiled two spatially extended velocity components; the velocity gap between them covers the same LSR velocities of the Sgr B2 dense cores. If HNCO is formed via surface reactions, the pervasive detection of HNCO in the outer edges of Sgr B2 cloud core leads to the cloud-cloud collision postulate. <P />A north-south C<SUP>18</SUP>O bipolar structure was seen in Sgr B2(M) centered at the compact H II region F. The bipolar structure appears asymmetric and thus favors the outflow interpretation. The sharp outer edges of the C<SUP>18</SUP>O line profiles of the two lobes further support the outflow picture. The estimated outflow age is ∼2±1 x 10<SUP>4</SUP> yr, and the total mass is ∼1700 M<SUB>sun</SUB>. The outflow masses for the blue and red lobes are &lt;360 M<SUB>sun</SUB> and &lt;410 M<SUB>sun</SUB>, respectively. The mass-loss rate is thus &lt;0.037 M<SUB>sun</SUB> yr<SUP>-1</SUP>. The detection of outflows in Sgr B2(M) supports the gas dispersal picture and subsequent chemical variations disclosed by the HNO and HC<SUP>13</SUP>CCN emission void. Three distinct velocity components toward Sgr B2(N) were seen from the HNCO K<SUB>-1</SUB> = 2 emission. The broad component is centered at the H II region K2 with a north-south velocity gradient, which is probably due to rotation. The mass of the rotating cloud is between ∼630 and 1570 M<SUB>sun</SUB>. The two narrow components are located on the opposite sides of the K1-K2 ridge and are in fact the two lobes of a gas outflow. The estimated outflow age of Sgr B2(N) is ∼6 x 10<SUP>3</SUP> yr, which is a factor of 3 younger than Sgr B2(M). The outflow masses are ≤200 and ≤300 M<SUB>sun</SUB> for the red and blue lobes, respectively. This yields a mass-loss rate &lt;0.08 M<SUB>sun</SUB> yr<SUP>-1</SUP>, about 2 times higher than that of Sgr B2(M). All these suggest that Sgr B2(N) is much younger than Sgr B2(M). Finally, high-resolution imaging of the radiatively excited HNCO K<SUB>-1</SUB> = 2 transition allows the separation of an apparent bipolar structure into a gas outflow and a rotating disk cloud.

U-Band Polarimetry of the Radio-aligned Optical Continuum in the Abell 1795 Cluster Central Galaxy

We have obtained U-band polarimetry of the lobes of blue optical continuum located along the z = 0.063 F-R I radio source in the Abell 1795 cluster central galaxy. We find an upper limit to the degree of polarization of the light emitted from the lobes of less than 7%. The accuracy of this measurement is limited by the presence of diluting background starlight. This limit is inconsistent with the lobes being scattered light that originated in an obscured, anisotropically radiating nucleus, Unless the radiation is beamed and is viewed at an angle &lt;~ 22^deg^ to the line of sight, which is unlikely. The absence of a polarized signal and detailed correspondence between the radio lobes and optical lobes is inconsistent with synchrotron light. The blue optical lobes are probably regions of recent star formation. If a burst of star formation were triggered by the expanding radio lobes, the age of the burst population should be ~10^7^ yr. Then, the star formation rate in both lobes, assuming the local IMF, is ~20 M_sun_ yr^-1^, and the stellar mass of the lobes is ~10^8^ M_sun_. The material fueling the star formation and the radio source may have originated from the cooling flow or accretion from one or more gaseous cluster galaxies.

The Dense Core, Outflow, and ``Jet'' in L810: High-Resolution Haystack Observations at 3 Millimeters

view Abstract Citations (5) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Dense Core, Outflow, and ``Jet'' in L810: High-Resolution Haystack Observations at 3 Millimeters Clemens, Dan P. ; Berkovitch, Michael ; Yun, Joao Lin ; Patel, Nimesh ; Xie, Taoling Abstract We have used the Haystack 37 m radio telescope to obtain high angular resolution spectral line maps of the innermost region of the star-forming Bok globule L810 (CB 205). These maps cover the central 1' x 1' region with a sampling interval of 8"-10". One map was obtained in the CO (J = 1-0) spectral line in order to identify the source(s) of the high-velocity gas. A CS (J = 2-1) map was obtained in order to find the location and kinematics of dense gas in this cloud core. Finally, a jetlike feature seen in near-infrared images was examined in two lines each of SO and SO2, to search for postshock chemical abundance enhancements. We find a bright 4-11 Msun CS core associated with both the IRS near-infrared stellar source (identified by Yun et al. 1993) and the IRAS 19433+2743 far-infrared point source. The red and blue CO outflow lobes do appear to originate from IRS/IRAS 19433+2743 and join with the larger scale CO lobes mapped by Xie & Goldsmith (1990). However, the outflow lobes are not symmetrically placed about the IRS source. Instead, the outflow lobes are both offset some 30" westward of the IRS position, producing a "swept-back" appearance. The abundance of SO is not enhanced in the region of the jetlike feature, although CS shows a local intensity maximum there. The apparent location of the near-infrared jetlike feature, in the middle of the newly resolved blue outflow lobe, may be due to either enhanced dust scattering from a preexisting cloud clump located within the outflow or it could signify the presence of a region influenced by a previous epoch of star formation within L810. Publication: The Astrophysical Journal Pub Date: February 1996 DOI: 10.1086/176769 Bibcode: 1996ApJ...457..743C Keywords: ISM: GLOBULES; ISM: INDIVIDUAL ALPHANUMERIC: L810; ISM: JETS AND OUTFLOWS; ISM: STRUCTURE; RADIO LINES: ISM full text sources ADS | data products SIMBAD (5)

Radio-Optical Alignments in Nearby Cooling Flow Cluster Central Galaxies

The centers of dominant cluster galaxies in cooling flows are often unusually blue, they have spatially extended nebular line emission and bright, FR I radio sources (Fabian 1994). As a class, they are the most rapidly evolving giant elliptical galaxies known. Among the most interesting of these objects, the Abell 1795 (z = 0.06) and Abell 2597 (z = 0.08) central cluster galaxies have very blue, lobe-like structures that are located along their FR I radio lobes (McNamara &amp; O'Connell 1993). This discovery was surprising because correlations between the radio source and blue optical continuum were thought to occur exclusively in powerful, FR II radio galaxies at redshifts z &gt; 0.6 that show the alignment effect. By analogy with the distant radio galaxies, the blue lobes are thought to be regions of star formation that were triggered by the passage of the radio source (De Young 1995), or scattered light from an obscured, anisotropically radiating active nucleus that is beaming its light obliquely to the line of sight (Sarazin &amp; Wise 1993; Crawford &amp; Fabian 1993; Sarazin et al. 1995). Scattered light is usually polarized. Therefore, polarization measurements of the aligned optical continuum should provide a strong test of the scattering hypothesis.McNamara et al. (1995) have obtained U-band polarimetry of the blue lobes in the Abell 1795 cluster central galaxy. They found an upper limit to the degree of polarization of the light emitted from the lobes of &lt; 7%. The accuracy of this measurement is limited by the presence of diluting background starlight. This limit is inconsistent with the lobes being scattered light that originated in an obscured, anisotropically radiating nucleus, unless the radiation is beamed and is viewed at an angle &lt; 22° to the line of sight, which is unlikely. The absence of a detailed correspondence between the radio lobes and optical lobes and the absence of a polarized signal is also inconsistent with synchrotron light.The blue optical lobes are probably regions of vigorous star formation. If a burst of star formation were triggered by the expanding radio lobes, the age of the burst population should be ≃ 107 yr. The star formation rate in both lobes, assuming the Local IMF, would then be ≃ 20 M⊙ yr–1 and the stellar mass of the lobes would be ≃ 108 M⊙. The large cooling flow in A1795 may be fueling the star formation and the radio source or the fuel may have originated from one or more gaseous cluster galaxies that recently fell into the cluster's core. This result strongly suggests that the radio sources in central cluster galaxies may be a significant factor driving the evolution of their stellar populations.

On the Origin of Blue Lobes in Central Cooling Flow Galaxies

view Abstract Citations (15) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Origin of Blue Lobes in Central Cooling Flow Galaxies De Young, David S. Abstract Recent observations of the central galaxy in two rich clusters with probable cooling flows have shown double-lobed distributions of blue light. In each case the blue light is coincident with the emission from a central double radio source. Moreover, in the one case so far observed, the blue continuum appears to be unpolarized. The possibility that this blue continuum is due to young stars produced by jet-induced star formation is explored here. Numerical simulation of the jet propagation through the ambient ISM, followed by shock-induced star formation and subsequent tracking of the stellar orbits in the galaxy and cluster potential allows a study of the development of the blue continuum as a function of space and time. It is found that agreement with observations can be obtained either if the radio jets are seen at an early stage (∼107 yr), with total energy fluxes of order 1044 ergs s-1, or if the jets are robust but short lived, with lifetimes less than 107 yr. In the first case these events must be intrinsically rare; if the second case is true, then the events can be more common and may account for the anomalous color gradients seen in central galaxies residing in rich clusters. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/175810 Bibcode: 1995ApJ...446..521D Keywords: GALAXIES: CLUSTERS: GENERAL; GALAXIES: COOLING FLOWS; GALAXIES: JETS; GALAXIES: PHOTOMETRY; GALAXIES: STRUCTURE full text sources ADS | data products SIMBAD (3)