NW Component Research Articles

The interstellar medium of dwarf galaxies: new insights from Machine Learning analysis of emission-line spectra

Dwarf galaxies are ideal laboratories to study the physics of the interstellar medium (ISM). Emission lines have been widely used to this aim. Retrieving the full information encoded in the spectra is therefore essential. This can be efficiently and reliably done using Machine Learning (ML) algorithms. Here, we apply the ML code GAME to MUSE (Multi Unit Spectroscopic Explorer) and PMAS (Potsdam Multi Aperture Spectrophotometer) Integral Field Unit (IFU) observations of two nearby Blue Compact Galaxies (BCGs): Henize 2-10 and IZw18. We derive spatially resolved maps of several key ISM physical properties. We find that both galaxies show a remarkably uniform metallicity distribution. Henize 2-10 is a star forming dominated galaxy, with a Star Formation Rate (SFR) of about 1.2 M$_{\odot}$ yr$^{-1}$. Henize 2-10 features dense and dusty ($A_V$ up to 5-7 mag) star forming central sites. We find IZw18 to be very metal-poor ($Z$= 1/20 $Z_{\odot}$). IZw18 has a strong interstellar radiation field, with a large ionization parameter. We also use models of PopIII stars spectral energy distribution as a possible ionizing source for the HeII $\lambda$4686 emission detected in the IZw18 NW component. We find that PopIII stars could provide a significant contribution to the line intensity. The upper limit to the PopIII star formation is 52% of the total IZw18 SFR.

The 2008 outburst in the young stellar system Z CMa

Context. Z CMa is a complex pre-main sequence binary with a current separation of 110 mas, known to consist of an FU Orionis star (SE component) and an embedded Herbig Be star (NW component). Although it represents a well-studied and characterized system, the origin of photometric variabilities, the component properties, and the physical configuration of the system remain mostly unknown. Aims. Immediately when the late-2008 outburst of Z CMa was announced to the community, we initiated a high angular resolution imaging campaign aimed at characterizing the outburst state of both components of the system in the near-infrared. Methods. We used the VLT/NACO and the Keck/NIRC2 near-infrared adaptive optics instrument to monitor the astrometric position and the near-infrared photometry of the Z CMa components during the outburst phase and one year after. The VLT/SINFONI and Keck/OSIRIS integral field spectroscrographs were in addition used to characterize for the first time the resolved spectral properties of the FU Orionis and the Herbig Be component during and after the outburst. Results. We confirm that the NW star dominates the system flux in the 1.1−3.8 μm range and is responsible for the photometric outburst. We extract the first medium-resolution (R ~ 2000−4000) near-infrared (1.1−2.4 μm) spectra of the individual components. The SE component has a spectrum typical of FU Orionis objects. The NW component spectrum is characteristic of embedded outbursting protostars and EX Or objects. It displays numerous emission lines whose intensity correlates with the system activity. In particular, we find a correlation between the Brγ equivalent width and the system brightness. The bluing of the continuum of the NW component along with the absolute flux and color-variation of the system during the outburst suggests that the outburst was caused by a complex interplay between a variation of the extinction in the line of sight of the NW component on one hand, and the emission of shocked regions close to the NW component on the other. We confirm the recently reported wiggling of the SE component jet from [Fe II] line emission. We find a point-like structure associated with a peak emission at 2.098 μm coincidental with the clump or arm seen in broadband polarization differential imaging as well as additional diffuse emission along a PA = 214°. The origin of these two structures is unclear and deserves further investigation.

INTRACLUSTER MEDIUM OF THE MERGING CLUSTER A3395

We present a detailed imaging and spectral analysis of the merging environment of the bimodal cluster A3395 using X-ray and radio observations. X-ray images of the cluster show five main constituents of diffuse emission : A3395 NE, A3395 SW, A3395 NW, A3395 W, and a filament connecting NE to W. X-ray surface-brightness profiles of the cluster did not show any shock fronts in the cluster. Temperature and entropy maps show high temperature and high entropy regions in the W, the NW, the filament and between the NE and SW subclusters. The NE, SW and W components have X-ray bolometric luminosities similar to those of rich clusters of galaxies but have relatively higher temperatures. Similarly, the NW component has X-ray bolometric luminosity similar to that of isolated groups but with much higher temperature. It is, therefore, possible that all the components of the cluster have been heated by the ongoing mergers. The NE subcluster is the most massive and luminous constituent and other subclusters are found to be gravitationally bound to it. The W component is most probably either a clump of gas stripped off the SW due to ram pressure or a separate subcluster that has merged or is merging with the SW. No X-ray cavities are seen associated with the Wide Angle Tailed (WAT) radio source near the centre of the SW subcluster. Minimum energy pressure in the radio emission-peaks of the WAT galaxy is comparable with the external thermal pressure. The radio spectrum of the WAT suggests a spectral age of ~10Myr.

THE 2008 OUTBURST IN THE YOUNG STELLAR SYSTEM Z CMa: THE FIRST DETECTION OF TWIN JETS

The Z CMa binary is understood to undergo both FU Orionis (FUOR) and EX Orionis (EXOR) type outbursts. While the SE component has been spectro- scopically identified as an FUOR, the NW component, a Herbig Be star, is the source of the EXOR outbursts. The system has been identified as the source of a large outflow, however, previous studies have failed to identify the driver. Here we present adaptive optics (AO) assisted [FeII] spectro-images which reveal for the first time the presence of two jets. Observations made using OSIRIS at the Keck Observatory show the Herbig Be star to be the source of the parsec-scale outflow, which within 2'' of the source shows signs of wiggling and the FUOR to '' be driving a ~ 0.4 jet. The wiggling of the Herbig Be star's jet is evidence for an additional companion which could in fact be generating the EXOR outbursts, the last of which began in 2008 (Grankin & Artemenko 2009). Indeed the dy- namical scale of the wiggling corresponds to a time-scale of 4-8 years which is in agreement with the time-scale of these outbursts. The spectro-images also show a bow-shock shaped feature and possible associated knots. The origin of this structure is as of yet unclear. Finally interesting low velocity structure is also observed. One possibility is that it originates in a wide-angle outflow launched from a circumbinary disk.

Changes in monsoon and ocean circulation and the vegetation cover of southwest Sumatra through the last 83,000 years: The record from marine core BAR94-42

We present the palynological record from deep-sea core BAR94-42 taken offshore of southwest Sumatra in the Indian Ocean. Refinement of a previous age model for the core has been made using 7 additional radiocarbon ages and 29 additional oxygen-isotope measurements. These analyses have substantially improved the previously published chronology, which has enabled revision of the results of sedimentological studies of the core. The pollen and re-interpreted biogenic and terrigeneous data were used to reconstruct monsoon circulation and vegetation of southwest Sumatra over the last 83,000 years (83 kyr). During marine isotope stage (MIS) 5a, southwest Sumatra was covered by rainforest, with open herbaceous swamps lining river courses and surrounding lakes. The SE component of the monsoon was stronger than the NW component, resulting in a humid climate with a short, dry season. During MIS 4, conditions were drier, fire activity increased and the monsoon was generally weaker. This latter pattern persisted until MIS1. The vegetation was most open during MIS 3, between ~ 52 and 43 kyr; identifying this phase as the driest of the last glacial. An increase in montane trees from ~ 52 kyr indicates the onset of cooler conditions, which lasted until the transition to MIS 1 at about 11.9 kyr. After ~ 43 kyr, an everwet climate gradually developed as monsoonal circulation intensified and the SE monsoon component became stronger. During this time, closed-canopy rainforest became dominant regionally over southwest Sumatra. Increased monsoonal activity during the early Holocene resulted in increased precipitation, river runoff, sediment discharge and offshore sediment transport from the continental shelf.

The nature of the recent extreme outburst of the Herbig Be/FU Orionis binary Z Canis Majoris,

Z CMa is a binary system which consists of two young stars: A Herbig AeBe component "Z CMa NW" embedded in a dust cocoon and a less massive component "Z CMa SE", which is classified as a FU Orionis type star. Recently, the system showed the largest outburst reported during the almost 90 years of available observations. During the recent outburst we detect that the Z CMa system is polarized by 2.6% in the continuum and emission line spectrum, with a position angle still perpendicular to the jet. From the high level of polarization we conclude that the outburst is associated with the dust embedded Herbig AeBe NW component. The main result of our studies is that the bolometric luminosity of Z CMa remained surprisingly constant during the recent "outburst". We conclude that either the geometry of the cavity through which the light escapes from the cocoon has opened a new path, or that the screen of dust, which reflects the light toward the observer became more efficient causing the observed increase of the visual brightness by about 2.5 magnitudes.

DISENTANGLING THE CIRCUMNUCLEAR ENVIRONS OF CENTAURUS A. I. HIGH-RESOLUTION MOLECULAR GAS IMAGING

We present high resolution images of the 12CO(2-1) emission in the central 1' (1 kpc) of NGC 5128 (Centaurus A), observed using the SMA. We elucidate for the first time the distribution and kinematics of the molecular gas in this region with a resolution of 6'.0 x 2'.4 (100 pc x 40 pc). We spatially resolve the circumnuclear molecular gas in the inner 24'' x 12'' (400 pc x 200 pc), which is elongated along a position angle P.A. = 155 deg and perpendicular to the radio/X-ray jet. The SE and NW components of the circumnuclear gas are connected to molecular gas found at larger radii. This gas appears as two parallel filaments at P.A. = 120 deg, which are coextensive with the long sides of the 3 kiloparsec parallelogram shape of the previously observed dust continuum, as well as ionized and pure rotational H2 lines. Spatial and kinematical asymmetries are apparent in both the circumnuclear and outer gas, suggesting non-coplanar and/or non-circular motions. We extend to inner radii (r < 200 pc) previously studied warped disk models built to reproduce the central parallelogram-shaped structure. Adopting the warped disk model we would confirm a gap in emission between the radii r = 200 - 800 pc (12'' - 50''), as has been suggested previously. Although this model explains this prominent feature, however, our 12CO(2-1) observations show relevant deviations from this model. Namely, the physical connection between the circumnuclear gas and that at larger radii, brighter SE and NW sides on the parallelogram-shaped feature, and an outer curvature of its long sides. Overall it resembles more closely an S-shaped morphology, a trend that is also found in other molecular species. Hence, we explore qualitatively the possible contribution of a weak bi-symmetric potential which would naturally explain these peculiarities.

Postflexion larvae and juvenile daily growth patterns of the Albor&amp;aacute;n Sea sardine (&lt;em&gt;Sardina pilchardus&lt;/em&gt; Walb.): influence of wind

The Alboran Sea is a hydrographically complex and variable area in which wind-driven coastal upwelling occurs. Its most abundant small pelagic resource is the sardine ( Sardina pilchardus ), which is subject to major interannual oscillations. Postflexion stages of sardine larvae were sampled in their main nursery grounds in the north Alboran Sea, and sardine juveniles were sampled periodically throughout the recruitment season. Daily growth analysis was used to identify periods favourable for larval survival and to assess the evolution of daily increment widths during the first months of life. The results showed that juveniles born later in the spawning season grew relatively faster than those born earlier. Two main growth phases were observed in juveniles: an initial one in which daily increment widths increased progressively, and a second one in which widths fluctuated, showing a decreasing trend. The beginning of the second phase was almost synchronous among different sub-cohorts, suggesting that it was triggered by environmental factors. The estimated mean daily growth rates during the larval phase were higher in surviving juveniles than in postflexion larvae born in the same month, supporting the “bigger is better” hypothesis in relation to larval survival. The influence of the environmental regime on growth was explored, and the evolution of a growth-related index, derived from otolith increment width variability, was compared with a single environmental descriptor, a “wind index” based on wind stress and direction. This analysis suggested that larval survival and larval and juvenile growth rates showed a positive correlation with NW component winds, associated with upwelling events on the continental shelf and calm sea weather conditions in the inshore nursery grounds. Conversely, Levantine and southern wind periods, which interrupt the upwelling and create rough seas in the inshore bays, lead to a decrease in growth rates in juveniles and low larval survival.

Spectroscopic properties and dynamical evolution of the merging system AM 1003-435

Aims. We study the system AM 1003-435, which is composed of two strong interacting galaxies. Methods. We obtained long-slit optical spectra of twelve zones of the system, and performed numerical simulations of the encounter between the components following the evolution of their stellar and gaseous contents. Results. The spectrum of the NW nucleus is typical of a starburst, while that of the SE one shows weak emission lines. The highest values of the oxygen and nitrogen abundances are at the NW nucleus. Its derived Hα and Hα + [N II] equivalent widths indicate very intense star formation, in accord to its starburst nature. Indicative ages of the starbursts in the nuclei were obtained. The morphological types of both components derived from their spectral characteristics are in agreement with previous determinations based on photometric parameters. About 70% of the measured Hα luminosity would correspond to the NW component contribution. The IR luminosity of the system is not high (LIR < 10 11 L� ). The estimated star formation rate for AM 1003-435 indicates that its activity is also moderate. The IR radiation, if it has the same origin as the Hα emission, would arise mostly from the NW component. The resulting abundances, burst ages, and masses suggest that the starburst in the SE component, the minor one, started earlier than that of the NW one, and did so in a medium poorer in weighted elements. On the other hand, from a set of N-body simulations of the encounter between both components it was found the time of the perigalacticum, to be comparable to the burst age derived for the SE component, and the star formation in both galaxies would have begun after the perigalacticum. It was also estimated that the central bodies will merge in about 1 Gyr.

Helium Abundance in the Most Metal‐deficient Blue Compact Galaxies: I Zw 18 and SBS 0335−052

We present high-quality spectroscopic observations of the two most-metal deficient blue compact galaxies known, I Zw 18 and SBS 0335-052 to determine the helium abundance. The underlying stellar absorption strongly influences the observed intensities of He I emission lines in the brightest NW component of I Zw 18, and hence this component should not be used for primordial He abundance determination. The effect of underlying stellar absorption, though present, is much smaller in the SE component. Assuming all systematic uncertainties are negligible, the He mass fraction derived in this component is Y = 0.243+/-0.007. The high signal-to-noise ratio spectrum (> 100 in the continuum) of SBS 0335-052 allows us to measure the helium mass fraction with a precision better than 2% -- 5% in nine different regions along the slit. Assuming all systematic uncertainties are negligible, the weighted mean He mass fraction in SBS 0335-052 is Y = 0.2437+/-0.0014 when the three He I 4471, 5876 and 6678 emission lines are used, and is 0.2463+/-0.0015 when the He I 4471 emission line is excluded. The weighted mean helium mass fraction in the two most metal-deficient BCGs I Zw 18 and SBS 0335-052, Y=0.2462+/-0.0015, after correction for the stellar He production results in a primordial He mass fraction Yp = 0.2452+/-0.0015. The derived Yp leads to a baryon-to-photon ratio of (4.7+/-1.0) 10^{-10}, consistent with the values derived from the primordial D and 7Li abundances, and supporting the standard big bang nucleosynthesis theory. For the most consistent set of primordial D, 4He, and 7Li abundances we derive an equivalent number of light neutrino species 3.0+/-0.3 (95% C.L.).

Helium Abundance in the Most Metal-Deficient Dwarf Galaxies

AbstractThe high-quality long-exposure spectroscopic observations of the two most-metal deficient blue compact galaxies I Zw 18 and SBS 0335–052 are discussed. We confirm previous findings that underlying stellar absorption strongly influences the observed intensities of He I emission lines in the brightest NW component of I Zw 18, and hence this component should not be used for primordial He abundance determination. The effect of underlying stellar absorption, though present, is much smaller in the SE component. The extremely high signal-to-noise ratio spectrum (≥ 100 in the continuum) of the BCG SBS 0335–052 allows us to measure the helium mass fraction with precision better than 2% in nine different regions along the slit. The weighted mean of helium mass fraction in two most metal-deficient BCGs I Zw 18 and SBS 0335–052, Y=0.2462±0.0009, after correction for the He production in massive stars results in primordial He mass fraction Yp = 0.2452±0.0009.

I Z[CLC]w[/CLC] 18: A New Wolf-Rayet Galaxy

We report the discovery of broad Wolf-Rayet emission lines in the Multiple Mirror Telescope (MMT) spectrum of the NW component of I Zw 18, the lowest-metallicity blue compact dwarf (BCD) galaxy known. Two broad Wolf-Rayet (W-R) bumps at the wavelengths $\lambda$4650 and $\lambda$5800 are detected indicating the presence of WN and WC stars. The total numbers of WN and WC stars inferred from the luminosities of the broad He II $\lambda$4686 and C IV $\lambda$5808 lines are equal to 17(+/-)4 and 5(+/-)2, respectively. The W-R to O stars number ratio is equal to about 0.02, in satisfactory agreement with the value predicted by massive stellar evolution models with enhanced mass loss rates. The WC stars in the northwest component of I Zw 18 can be responsible for the presence of the nebular He II $\lambda$4686 emission line, however the observed intensity of this line is several times larger than model predictions, and other sources of ionizing radiation at wavelengths shorter than 228\AA are necessary.

High resolution fabry-perot and multi-pupil spectral observations of the genuine blue compact dwarf galaxy IZW18

We present the observations of the BCDG IZW18 performed with a Fabry-Perot interferometer at the CFH 3.6 m telescope and with a multi-pupil spectrograph at the SAO (Russia) 6 m telescope. The morphological structure of the galaxy in emission lines and in continuum, the velocity field of the ionized gas, and [OIII]/H β ratio distribution along the NW component have been investigated. Besides the NW and SE HII components, we find a population of small HII regions. Continuum maps show that the peaks of the stellar light distribution are displaced with respect to the emission lines maxima. the velocity field shows peculiar motions superposed on an approximately regular background implying solid body rotation. Emission line profiles exhibit an asymmetric structure, except for the NW compact component. The [OIII]/H β ratio decreases from the center of the NW component to its edge with the gradient of 1.86 kpc−1.

The Serpens Radio Jet: evidence of precession of nutation

Previous VLA observations of the triple radio continuum source in Serpens showed that it has very unusual and extraordinary characteristics. While this source is associated with a star forming region, its outer components exhibit a combination of thermal and nonthermal spectra and large proper motions, Furthermore, the NW lobe has knotty and extended emission connecting the central source with the bright outer knot. Here, we present results of new VLA radio continuum high-angular resolution observations of this Radio Jet. Combining these observations with those obtained previously, we find that: a) one of the knots along the main body of the radio jet (knot G) exhibits proper motions similar to those observed in the outer NW and SE components, and the time variable knot A; b) the outer knots are moving away from the central source in slightly different directions; and c) the orientation of the central source seems to change with time. These results are consistent with a central precessing source that undergoes periodic ejection of material.

Spatially resolved optical and near-infrared spectroscopy of I ZW 18

Long-slit optical and near-IR spectroscopy are presented for the bright NW and faint SE components of the oxygen-poor H II galaxy I Zw 18, yielding physical conditions and O, N, S, and He abundances for these components. All of the elemental abundances for the two components of I Zw 18 are equal (within errors), thereby placing constraints on evolutionary theories for this system.

Polarization maps of Cygnus A at 23 gigahertz

We present polarization maps with 6''.4 x 10''.7 resolution. The total intensity distributiin is dominated by the compact heads. The flux of the central source is 0.8 +- 0.15 Jy. The polarization distribution of the two lobes are quite similar. For both, the tails show smooth, large-scale structure and reach at least 30% linear polarization in places.Comparison with a 5 GHz map shows that the spectral index varies from -1 on the heads to less than -1.7 inward along the tails. This gradient is interpreted in terms of synchrotron losses occurring in the relativistic plasma as it flows out from the heads.For the NW component, comparison of the position angles of the polarized emission at 5 GHz with our maps shows changes in the amount of rotation of +- 45/sup 0/ with angular scales of approx.1'', but little depolarization at 5 GHz. The latter suggests that the thermal electron density within this lobe is at most 10/sup -3/ cm/sup -3/. The SE tail is highly depolarized at 5 GHz. We suggest that the polarization behavior of both components is perhaps caused by a lumpy Faraday rotating screen in the vicinity of the galaxy but outside the radio lobes.