Mild Starburst Research Articles

Refractive lens exchange for a multifocal intraocular lens with a surface-embedded near section in mild to moderate anisometropic amblyopic patients

To evaluate visual and refractive outcomes in amblyopic patients who had bilateral implantation of a multifocal intraocular lens (IOL) with a surface-embedded near section. Cathedral Eye Clinic, Belfast, Northern Ireland, United Kingdom. Comparative case series. Anisometropic amblyopic patients having bilateral implantation of Lentis Mplus multifocal IOLs were examined for distance and near visual acuities, contrast sensitivity, defocus curves, extent of crowding, reading speed, stereoacuity, and Quality of Vision (QoV) questionnaire scores preoperatively and at 3-month intervals during 12 months. A +3.00 diopter (D) reading addition IOL was used in all eyes. Twenty-eight eyes (14 patients) (mean age 59.4 years) were included. In the nonamblyopic eye, the mean uncorrected distance visual acuity (UDVA) was 0.16 logMAR ± 0.17 (SD), the mean corrected distance visual acuity (CDVA) was 0.02 ± 0.07 logMAR, and the mean near acuity was M 0.5 (Jaeger [J] 2 = logRAD 0.1) or better. In the amblyopic eye, the means were 0.30 ± 0.14 logMAR, 0.21 ± 0.11 logMAR, and M 0.8 (J4 = logRAD 0.3) or better, respectively. Bilateral reading speeds (mean 137.73 ± 28.7 words per minute [wpm]) surpassed unilateral nonamblyopic eye speeds (mean 130.6 ± 29.4 wpm). The mean QoV scores improved from 7.78 ± 10.23 preoperatively to 1.92 ± 5.21 at 12 months. No glare or halos were reported; 1 patient had mild starburst symptoms at 1 year. Patients rated distance and near vision as excellent. Anisometropic amblyopic patients may benefit from bilateral implantation of the multifocal IOL; no unwanted side effects were detected.

SPITZERVIEW OF YOUNG MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD H II COMPLEX N 44

The HII complex N44 in the Large Magellanic Cloud (LMC) provides an excellent site to perform a detailed study of star formation in a mild starburst, as it hosts three regions of star formation at different evolutionary stages and it is not as complicated and confusing as the 30 Doradus giant HII region. We have obtained Spitzer Space Telescope observations and complementary ground-based 4m uBVIJK observations of N44 to identify candidate massive young stellar objects (YSOs). We further classify the YSOs into Types I, II, and III, according to their spectral energy distributions (SEDs). In our sample of 60 YSO candidates, ~65% of them are resolved into multiple components or extended sources in high-resolution ground-based images. We have modeled the SEDs of 36 YSOs that appear single or dominant within a group. We find good fits for Types I and I/II YSOs,but Types II and II/III YSOs show deviations between their observed SEDs and models that do not include PAH emission. We have also found that some Type III YSOs have central holes in their disk components. YSO counterparts are found in four ultracompact HII regions and their stellar masses determined from SED model fits agree well with those estimated from the ionization requirements of the HII regions. The distribution of YSOs is compared with those of the underlying stellar population and interstellar gas conditions to illustrate a correlation between the current formation of O-type stars and previous formation of massive stars. Evidence of triggered star formation is also presented.

IC 5063: AGN driven outflow of warm and cold gas

We present new ATCA 17- and 24- GHz radio images and ESO- NTT optical spectra of the radio- loud Seyfert galaxy IC 5063, the first galaxy in which a fast (similar to 600 km s(-1)) outflow of neutral hydrogen was discovered. The new radio data confirm the triple radio structure with a central, unresolved flat- spectrum core and two resolved radio lobes with steep spectral index. This implies that the previously detected fast outflow of neutral gas is occurring off- nucleus, near a radio lobe about 0.5 kpc from the core. The ionised gas shows highly complex kinematics in the region co- spatial with the radio emission. Broad and blueshifted (similar to 500 km s(-1)) emission is observed in the region of the radio lobe, at the same location as the blueshifted Hi absorption. The velocity of the ionised outflow is similar to the one found in Hi. The first order correspondence between the radio and optical properties suggests that the outflow is driven by the interaction between the radio jet and the ISM. However, despite the high outflow velocities, no evidence is found for the ionisation of the gas being due to fast shocks in the region of the outflow, indicating that photoionisation from the AGN is likely to be the dominant ionisation mechanism. The outflow rate of the warm ( ionised) gas is small compared to that of the cold gas, similar to what is found in other radio galaxies. The mass outflow rate associated with the Hi is in the same range as for mild starburst- driven superwinds in ULIRGs. However, in IC 5063, the AGN- driven outflow appears to be limited to the inner kpc region of the galaxy. The kinetic power associated with the Hi outflow is a small fraction (a few x 10(-4)) of the Eddington luminosity of the galaxy but is a significant fraction (similar to 0.1) of the nuclear bolometric luminosity. In IC 5063, the observed outflows may have sufficient kinetic power to have a significant impact on the evolution of the ISM in the host galaxy.

Galactic star formation rates gauged by stellar end-products

Young galactic X-ray point sources (XPs) closely trace the ongoing star formation in galaxies. From measured XP number counts we extract the collective 2-10 keV luminosity of young XPs, L_yXP, which we use to gauge the current star-formation rate (SFR) in galaxies. We find that, for a sample of local star-forming galaxies (i.e., normal spirals and mild starbursts), L_yXP correlates linearly with the SFR over three decades in luminosity. A separate, high-SFR sample of starburst ULIRGs can be used to check the calibration of the relation. Using their (presumably SF-related) total 2-10 keV luminosities we find that these sources satisfy the SFR-L_yXP relation, as defined by the weaker sample, and extend it to span about 5 decades in luminosity. The SFR-L_yXP relation is likely to hold also for distant Hubble Deep Field North galaxies, especially so if these high-SFR objects are similar to the (more nearby) ULIRGs. It is argued that the SFR-L_yXP relation provides the most adequate X-ray estimator of instantaneous SFR by the phenomena characterizing massive stars from their birth (FIR emission from placental dust clouds) through their death as compact remnants (emitting X-rays by accreting from a close donor). For local, low/intermediate-SFR galaxies, the simultaneous existence of a correlation of the instantaneous SFR with the total 2-10 keV luminosity, which traces the SFR integrated over (approximately) the last Gyr, suggests that during such epoch the SF in these galaxies has been proceeding at a relatively constant rate.

CO, 13CO, and [CI] in Galaxy Centers

Measurements of [CI], (J=2-1) 13CO and (J=4-3) 12CO emission from quiescent, starburst and active galaxy centers reveal a distinct pattern characterized by relatively strong [CI] emission. The [CI] to 13CO emission ratio increases with central [CI] luminosity. It is lowest in quiescent and mild starburst centers and highest for strong starburst centers and active nuclei. Neutral C abundances are close to, or even exceed, CO abundances. The emission is characteristic of warm and dense gas rather than either hot tenuous or cold very dense gas. The relative intensities of CO, [CI], [CII] and far-infrared emission suggest that the dominant excitation mechanism in galaxy centers may be different from that in Photon-Dominated Regions (PDRs).

Evolutionary spectral energy distribution diagnostics of starburst galaxies: signature of bimodality

We construct an evolutionary spectral energy distribution (SED) model of a starburst region, from the ultraviolet to submillimetre wavelengths. This model allows us to derive the star formation rate, optical depth by dust and apparent effective radius of starburst regions at various wavelengths; as a result, the intrinsic surface brightness of starburst regions can be derived. Using this SED model, we analyse 16 ultraviolet-selected starburst galaxies and 10 ultraluminous infrared galaxies. The derived star formation rates and optical depths are compared with emission-line measurements and are found to be consistent. The derived apparent effective radii are also consistent with observations. From the SED analysis, we find a bimodal property of the star formation rate with the optical depth and the compactness of stellar distributions. While mild starbursts have a limiting intrinsic surface brightness L b o l r e - 2 ≃ 10 1 2 L⊙ kpc - 2 , intense starbursts tend to be more heavily obscured and concentrated within a characteristic scale of r e ≃ 0.3 kpc. We suggest that the mild starbursts can be triggered by a self-gravitating disc instability in which feedback is effective in the shallow gravitational potential. On the other hand, the intense starbursts can be induced via an external dynamical perturbation such as galaxy merging, in which feedback is less effective owing to the deep gravitational potential attained by the large gas concentration within the central starburst region.

Neutral atomic carbon in centers of galaxies

We present measurements of the emission from the centers of fifteen spiral galaxies in the 3 P 1 - 3 P 0 [CI] fine-structure transition at 492 GHz. Observed galaxy centers range from quiescent to starburst to active. The intensities of neutral carbon, the J = 2-1 transition of 1 3 CO and the J = 4-3 transition of 1 2 CO are compared in matched beams. Most galaxy centers emit more strongly in [CI] than in 1 3 CO, completely unlike the situation pertaining to Galactic molecular cloud regions. [CI] intensities are lower than, but nevertheless comparable to J = 4-3 1 2 CO intensities, again rather different from Galactic sources. The ratio of [CI] to 1 3 CO increases with the central [CI] luminosity of a galaxy; it is lowest for quiescent and mild starburst centers, and highest for strong starburst centers and active nuclei. Comparison with radiative transfer model calculations shows that most observed galaxy centers have neutral carbon abundances close to, or exceeding, carbon monoxide abundances, rather independent from the assumed model gas parameters. The same models suggest that the emission from neutral carbon and carbon monoxide, if assumed to originate in the same volumes, arises from a warm and dense gas rather than a hot and tenuous, or a cold and very dense gas. The observed [CI] intensities together with literature [CII] line and far-infrared continuum data likewise suggest that a significant fraction of the emission originates in medium-density gas (n = 10 3 -10 4 cm - 3 ), subjected to radiation fields of various strengths.

Recent star formation in the interacting galaxy system NGC 520

New optical spectroscopy, near-infrared spectroscopy, and mid-infrared imaging of the interacting system NGC 520 are presented. The data show that the heavily obscured primary nucleus has a current star-forming rate about 35 times the typical rate for a late-type galaxy nucleus, which may account for most of the large far-infrared luminosity of NGC 520. The secondary nucleus has little current star formation but has recently undergone a mild starburst. Optical colors and absorption line equivalent widths suggest that the extranuclear regions in both galaxies have experienced enhanced star formation roughly at the same time as the secondary nucleus, though at a lesser intensity. The extent of the extranuclear burst is large; at least half of the projected surface area of the two disks took part to varying degrees in the episode. Determining the exact age and strength of the recent star-formation episode in NGC 520 is uncertain. The best estimate for the initiation time of about few x 10 exp 8 yrs ago is consistent with the system-wide starburst being caused by the galaxy collision.