Herbig-Haro (HH) objects are small nebulous regions of shock excited gas associated with bipolar outflows from newly formed stars. This dissertation presents an extensive set of observational data on Herbig-Haro objects, including deep CCD images, medium resolution long-slit spectra, and high resolution echelle spectra. The CCD survey indicates that HH objects cannot be identified reliably on the basis of morphology alone. The spectral line data show that HH objects exhibit enormous linewidths even though the objects are only about 1500 AU in size. The spectra sometimes have two velocity peaks, and show spatial separation of the high and low radial velocity gas. A radiative bowshock model constructed from a series of planar shock models accounts for the large linewidths, unusual line profiles, line ratios, and spatial structure seen in HH objects. A simple formula is derived that relates the shock velocity and orientation angle of a radiating bowshock to the observed maximum and minimum radial velocities seen in a line profile. The bowshock forms around a 'bullet' of material ejected from the forming star. The most likely acceleration mechanism for the bullet seems to be a breakup of a collimated stellar jet.

A survey of the Monoceros OB1 dark cloud has been made for molecular outflows and young stellar objects. In all, nine molecular outflows and thirty far-infrared sources were identified in a portion of the cloud composed of about 3 x 10⁴ M(⊙)of material. Statistical arguments suggest that 90% of the far-infrared sources actually are young stellar objects embedded in the cloud. If the star formation rate in the Mon OB1 cloud is roughly constant with time then molecular outflows in the cloud should be able to support it against collapse due to gravity. This suggests that the birthrate of outflows in the solar neighborhood is very high. In fact, regardless of considerations of cloud support, the large number of outflows identified in the Mon OB1 cloud and the propensity of the youngest stellar objects in the cloud to be associated with outflows suggest that outflows have a high birthrate in the solar neighborhood and are part of a common stage in early stellar evolution. The young stellar objects identified in the cloud can be fit into a spectral classification system. In fact, in terms of spectral slopes, far-infrared luminosity, and source size the properties of the objects are consistent with expectations if the system represents an evolutionary sequence. It is also found that the outflow phase in early stellar evolution tends to occur at about the time that young stellar objects lose a large fraction of their circumstellar envelopes. As a result it seems likely that outflows play an important role in sweeping out the circumstellar gas around many young stellar objects and may, in fact, play an important part in the evolutionary transition between the protostellar and stellar stages of evolution.

We present a near-infrared study of the stars forming in the ρ Ophiuchi dark cloud and a mid- to far-infrared study of their environment. We determine that the total cloud luminosity matches that of the known embedded sources, ruling out the existence of a numerous but faint low mass embedded population. IRAS and optically thin C¹⁸O column density data are used to evaluate dust grain sizes and compositions via competing grain models. Radiative modleing shows that a standard power law distribution of graphite and silicate grains is responsible for IRAS 60 and 100 μm band emissions. These grains are heated to about one tenth of the cloud's depth in the core region. Their optical depths closely follow molecular column density structure, but these grains are considerably colder than the molecular gas. We detect 481 sources in the J,H, or K bands in a 0.184 deg.² survey region in the cloud. Approximately 79% of the embedded 3 band (JHK) detected sources have near-infrared color indices greater than the local background population, suggesting that many of these objects are in pre-main-sequence evolutionary phases. The reddest of these sources are grouped in a high column and spatial density area within the survey region. Sources in this area have a normal power-law K luminosity function which is consistent with a theoretical model of a standard mass function and an age of 10⁵ yr. Sources exterior to this area have a luminosity function with an excess of intermediate luminosity sources that significantly differs from the luminosity function of the interior region. We interpret this non-standard luminosity function and the wide range of source reddenings in this peripheral region to be indicators of a considerable age (10⁶ yr) or age spread among sources there. We estimate that the cloud's star formation efficiency is currently greater than or equal to 25%. These newly discovered young stellar sources provide a statistically significant sample for studies of the cloud's embedded population and support established ideas of bound cluster formation and star formation bursts within the cloud.

We present new HST/WFC3-IR narrow-band [Fe II] images of protostellar jets in the Carina Nebula. Combined with five previously published sources, we have a sample of 18 jets and two Herbig-Haro (HH) objects. All of the jets we targeted with Wide-Field Camera 3 (WFC3) show bright infrared [Fe II] emission, and a few Ha candidate jets are confirmed as collimated outflows based on the morphology of their [Fe II] emission. Continuum-subtracted images clearly separate jet emission from the adjacent ionization front, providing a better tracer of the collimated jet than Ha and allowing us to connect these jets with their embedded driving sources. The [Fe II] 1.64 mu m/Ha flux ratio measured in the jets is greater than or similar to 5 times larger than in the adjacent ionization fronts. The low-ionization jet core requires high densities to shield Fe+ against further ionization by the FUV radiation from O-type stars in the H II region. High jet densities imply high mass-loss rates, consistent with the intermediate-mass driving sources we identify for 13 jets. The remaining jets emerge from opaque globules that obscure emission from the protostar. In many respects, the HH jets in Carina look like a scaled-up version of the jets driven by low-mass protostars. Altogether, these observations suggest that [Fe II] emission is a reliable tracer of dense, irradiated jets driven by intermediate-mass protostars. We argue that highly collimated outflows are common to more massive protostars, and that they suggest the outflow physics inferred for low-mass stars formation scales up to at least similar to 8 M-circle dot.

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I present spectroscopic imaging of the high-velocity system (HVS) towards the central cD galaxy (NGC 1275) in the Perseus Cluster at a high spectral resolution for the first time. Previous observation suggests that the HVS is a highly inclined dusty and gas-rich galaxy moving towards the center of NGC 1275 at a high speed of 3000 km/s relative to the systemic velocity of NGC 1275 through the hot intracluster medium (ICM). If this is the case, then the HVS should be undergoing intense ram-pressure stripping. However, there is tentative evidence for ram-pressure stripping in the HVS, and furthermore confined to a small region of the galaxy. Previous observations also point out that at the location where the HVS is seen, there are many star clusters seen towards the inner region of NGC 1275. The separation of young star clusters between those belong to NGC 1275 and those belong to the HVS is, however, not clearly defined. The primary scientific objectives are to (i) search for evidence for ram-pressure stripping in the HVS, as well as signs of tidal interactions between the HVS and NGC 1275; and (ii) separate the numerous young star clusters seen towards the entire NGC 1275 into those associated with the HVS and those associated with NGC 1275. NGC 1275 and the HVS were observed simultaneously with the use of Potsdam Multi-Aperture Spectrophotometer. The main emission lines being studied are the Hα & [NII]λ6548,6483 lines in NGC 1275 and the HVS. I present maps of intensity distribution, velocity field and velocity dispersion of the Hαemission of the HVS, as well as the line ratio of the [NII] doublets lines to the Hα line in the HVS. I find that the line ratio of [NII]/Hα is less than 0.1 throughout the entire body of the HVS, indicating metallicity is low in the HVS. I also find that the metallicity is decreasing with distance from the center, just like other normal spiral galaxies. I demonstrate that a large fraction of the young star clusters seen towards the inner regions of NGC 1275 are closely associated with bright Hα-emitting regions in the HVS, and trace the overall Hα-emitting body of the HVS, suggesting that some young star clusters are associated to the HVS. I find that there are two distributions of young star clusters in color-color space, providing a way to separate out the star clusters likely belong to the HVS. I present evidence that the HVS is experiencing intense ram-pressure stripping and also evidence suggesting that the HVS is possibly tidally interacting with NGC 1275. The results demonstrate that the HVS is a dusty, gas-rich, low-metallicity galaxy that has been disrupted by ram-pressure stripping and possibly also tidal interactions. I show that the HVS exhibit widespread and vigorous (~3.6 MM_⊙ yr^(-1)) star formation over the last at least ~0.1 Gyr. The vigorous SFR of the HVS is in contrast to what suggested by the observed low metallicity (suggestive of relatively weak star-formation activity over the recent history). The SFR of the HVS is likely to be triggered by the same process that produces global distortion on the HVS, here ram pressure stripping and possibly tidal interaction are in consideration. / published_or_final_version / Physics / Master / Master of Philosophy

Molecular gas in other galaxies is generally studied by observations of CO emission; a conversion from CO integrated intensity to H₂ column density must be made. Modelling of the emission from an ensemble of molecular clouds shows that these conversion factors are sensitive to temperature, so that molecular gas masses in galaxies with high star formation rates have probably been overestimated. Conversely, models of molecular clouds in low metallicity systems (such as irregular galaxies) demonstrate that the use of CO as a tracer can severely underestimate the molecular gas abundance. The observed properties of dark clouds and high latitude clouds are consistent with clouds in equilibrium with an intercloud pressure of P/k ≈ 10⁴. Detailed comparison of the CO and 170μm emission from the disks of NGC 6946 and M51 shows that the far-infrared flux must arise from dust in molecular clouds, not atomic clouds; this emission may be powered by embedded young stars or by the interstellar radiation field. The interpretation of the ratio of infrared to CO luminosities as a star formation efficiency is of dubious validity. Modelling of the observed CO and far-infrared emission from a sample of galactic nuclei shows that roughly half of the CO flux is produced by very active star-forming clouds with warm CO. The constraints placed on star formation models by abundance gradients in galaxies suggests that radial gradients in star forming efficiency generally exist in galaxies. The actual distribution of molecular gas in galaxies may be closely tied to the radial mass distribution.

In this thesis we use multi-transitional millimeter/submillimeter-wave molecular spectroscopy of CO and CS to determine the state of the molecular gas in the central regions of three starbursts: M82, IC342, and M83. High angular resolution 60 and 100 μm IRAS images provide complementary information about the thermal dust emission in IC342 and M83. Our CO observations reveal the presence of a molecular ring and supernovae driven wind in M82. In IC342 and M83 there is evidence for molecular bars and central rotating cores. The CO and CS line ratio analyses suggest a multicomponenet medium with clouds externally heated by ultraviolet flux from young, massive stars. Excitation temperatures typically range from 20 to 40 K throughout the nuclear regions of the sample galaxies. In M82 the CO and CS optical depths are ∼ 1. Our analysis of ¹²CO indicates that this gas is optically thick toward the centers of IC342 and M83. The molecular gas mass in each galaxy is ∼ 5x10⁷ M(⊙). We derive an average cloud size between 0.1 and 1 pc in the nuclear region of M82 and M83. An average cloud size of 10 pc is found over a comparable region in IC342. From tidal arguments we find that the clouds must have densities greater than 100 to 1000 cm⁻³ to survive. If the clouds are virialized, then the expected individual cloud linewidths are 9, 40, 5 and 27 km/s for M82, IC342, M83 and the Milky Way, respectively. For the clouds to be pressure-bound, inter-cloud pressures > 10x the peak value in the Galactic Center are required. If the magnetic fields are frozen into the gas, an average field strength of 8.5 mG is needed to support the nuclear clouds in each galaxy from collapse. Enhanced IRAS images reveal bright, compact nuclear components in IC342 and M83. HII regions are seen along spiral arms in IC342 and a dusty bar is seen in M83. The similarity between radio continuum maps and the high resolution IRAS maps suggest that infrared emission arises from HII regions. Using an emissivity law of β ∼ 1.5, the derived dust temperatures in the nuclei of IC342 and M83 are essentially the same as the gas excitation temperatures. For this to occur, gas densities of > 10⁴ cm⁻³ are implied. We derive a star-formation efficiency, ∊, of 77, 60, 10 and 2% for M82, M83, IC342, and the Milky Way, respectively. We find evidence that the gas surface density toward the centers of these galaxies is α ∊. We estimate star-formation rates of 16, 6, 2.5, and .06 M(⊙)/yr for M82, M83, IC342 and the Milky Way. The gas depletion timescales are a few million years for M82 and M83 and a few times 10⁷ and 10⁸ years in IC342 and the Milky Way. We find a strong correlation between cloud diameter and star-formation efficiency, with smaller clouds found in galaxies with higher ∊. We conclude these smaller clouds are a by-product and not a causal factor of the starburst phenomenon.

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